AlTabayoyon

GlennWidener

ShigeruYamada

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files
(the “Software”), to deal in the Software without restriction,
including without limitation the rights to use, copy, modify, merge, publish,
distribute, sublicense, and/or sell copies of the Software, and to permit
persons to whom the Software is furnished to do so, subject to the following
conditions:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED “AS IS”, WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
OPEN GROUP BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

Except as contained in this notice, the name of The Open Group shall not
be used in advertising or otherwise to promote the sale, use or other dealings
in this Software without prior written authorization from The Open Group.

Permission to use, copy, modify and distribute this documentation for any
purpose and without fee is hereby granted, provided that the above copyright
notice appears in all copies and that both that copyright notice and this
permission notice appear in supporting documentation, and that the names of
Digital and Tetronix not be used in in advertising or publicity pertaining
to distribution of the software without specific, written prior permission.
Digital and Tetronix make no representations about the suitability of the
software described herein for any purpose.
It is provided “as is” without express or implied warranty.

Acknowledgments

The design and implementation of the first 10 versions of X
were primarily the work of three individuals: Robert Scheifler of the
MIT Laboratory for Computer Science and Jim Gettys of Digital
Equipment Corporation and Ron Newman of MIT, both at MIT
Project Athena.
X version 11, however, is the result of the efforts of
dozens of individuals at almost as many locations and organizations.
At the risk of offending some of the players by exclusion,
we would like to acknowledge some of the people who deserve special credit
and recognition for their work on Xlib.
Our apologies to anyone inadvertently overlooked.

Release 1

Our thanks does to Ron Newman (MIT Project Athena),
who contributed substantially to the
design and implementation of the Version 11 Xlib interface.

Our thanks also goes to Ralph Swick (Project Athena and Digital) who kept
it all together for us during the early releases.
He handled literally thousands of requests from people everywhere
and saved the sanity of at least one of us.
His calm good cheer was a foundation on which we could build.

Our thanks also goes to Todd Brunhoff (Tektronix) who was “loaned”
to Project Athena at exactly the right moment to provide very capable
and much-needed assistance during the alpha and beta releases.
He was responsible for the successful integration of sources
from multiple sites;
we would not have had a release without him.

Our thanks also goes to Al Mento and Al Wojtas of Digital's ULTRIX
Documentation Group.
With good humor and cheer,
they took a rough draft and made it an infinitely better and more useful
document.
The work they have done will help many everywhere.
We also would like to thank Hal Murray (Digital SRC) and
Peter George (Digital VMS) who contributed much
by proofreading the early drafts of this document.

Our thanks also goes to Jeff Dike (Digital UEG), Tom Benson,
Jackie Granfield, and Vince Orgovan (Digital VMS) who helped with the
library utilities implementation;
to Hania Gajewska (Digital UEG-WSL) who,
along with Ellis Cohen (CMU and Siemens),
was instrumental in the semantic design of the window manager properties;
and to Dave Rosenthal (Sun Microsystems) who also contributed to the protocol
and provided the sample generic color frame buffer device-dependent code.

The alpha and beta test participants deserve special recognition and thanks
as well.
It is significant
that the bug reports (and many fixes) during alpha and beta test came almost
exclusively from just a few of the alpha testers, mostly hardware vendors
working on product implementations of X.
The continued public
contribution of vendors and universities is certainly to the benefit
of the entire X community.

Our special thanks must go to Sam Fuller, Vice-President of Corporate
Research at Digital, who has remained committed to the widest public
availability of X and who made it possible to greatly supplement MIT's
resources with the Digital staff in order to make version 11 a reality.
Many of the people mentioned here are part of the Western
Software Laboratory (Digital UEG-WSL) of the ULTRIX Engineering group
and work for Smokey Wallace, who has been vital to the project's success.
Others not mentioned here worked on the toolkit and are acknowledged
in the X Toolkit documentation.

Of course,
we must particularly thank Paul Asente, formerly of Stanford University
and now of Digital UEG-WSL, who wrote W, the predecessor to X,
and Brian Reid, formerly of Stanford University and now of Digital WRL,
who had much to do with W's design.

Finally, our thanks goes to MIT, Digital Equipment Corporation,
and IBM for providing the environment where it could happen.

Release 4

We also thank Al Mento of Digital for his continued effort in
maintaining this document and Jim Fulton and Donna Converse (MIT X Consortium)
for their much-appreciated efforts in reviewing the changes.

We also once again thank Al Mento of Digital for his work in formatting
and reformatting text for this manual, and for producing man pages.
Thanks also to Clive Feather (IXI) for proof-reading and finding a
number of small errors.

Release 7

This document is made available to you in modern formats such as HTML and PDF
thanks to the efforts of Matt Dew, who converted the original troff sources to
DocBook/XML and edited them into shape; along with Gaetan Nadon and
Alan Coopersmith, who set up the formatting machinery in the libX11 builds and
performed further editing of the DocBook markup.

The X Window System is a network-transparent window system that was
designed at MIT. X display servers run on computers with either
monochrome or color bitmap display hardware. The server distributes
user input to and accepts output requests from various client programs
located either on the same machine or elsewhere in the network. Xlib
is a C subroutine library that application programs (clients) use to
interface with the window system by means of a stream connection.
Although a client usually runs on the same machine as the X server
it is talking to, this need not be the case.

Xlib − C Language X Interface is a reference
guide to the low-level C language interface to the X Window System
protocol. It is neither a tutorial nor a user’s guide to programming
the X Window System. Rather, it provides a detailed description of
each function in the library as well as a discussion of the related
background information. Xlib − C Language X Interface
assumes a basic understanding of a graphics window system and of the C
programming language. Other higher-level abstractions (for example,
those provided by the toolkits for X) are built on top of the Xlib
library. For further information about these higher-level libraries,
see the appropriate toolkit documentation.
The X Window System Protocol provides the
definitive word on the behavior of X.
Although additional information appears here, the protocol document is
the ruling document.

Overview of the X Window System

Some of the terms used in this book are unique to X,
and other terms that are common to other window systems
have different meanings in X. You may find it helpful to refer to
the glossary,
which is located at the end of the book.

The X Window System supports one or more screens containing
overlapping windows or subwindows.
A screen is a physical monitor and hardware
that can be color, grayscale, or monochrome.
There can be multiple screens for each display or workstation.
A single X server can provide display services for any number of screens.
A set of screens for a single user with one keyboard and one pointer
(usually a mouse) is called a display.

All the windows in an X server are arranged in strict hierarchies.
At the top of each hierarchy is a root window,
which covers each of the display screens.
Each root window is partially or completely covered by child windows.
All windows, except for root windows, have parents.
There is usually at least one window for each application program.
Child windows may in turn have their own children.
In this way,
an application program can create an arbitrarily deep tree
on each screen.
X provides graphics, text, and raster operations for windows.

A child window can be larger than its parent.
That is, part or all of
the child window can extend beyond the boundaries of the parent,
but all output to a window is clipped by its parent.
If several children of a window have overlapping locations,
one of the children is considered to be on top of or raised over the
others, thus obscuring them.
Output to areas covered by other windows is suppressed by the window
system unless the window has backing store.
If a window is obscured by a second window,
the second window obscures only those ancestors of the second window
that are also ancestors of the first window.

A window has a border zero or more pixels in width, which can
be any pattern (pixmap) or solid color you like.
A window usually but not always has a background pattern,
which will be repainted by the window system when uncovered.
Child windows obscure their parents,
and graphic operations in the parent window usually
are clipped by the children.

Each window and pixmap has its own coordinate system.
The coordinate system has the X axis horizontal and the Y axis vertical
with the origin [0, 0] at the upper-left corner.
Coordinates are integral,
in terms of pixels,
and coincide with pixel centers.
For a window,
the origin is inside the border at the inside, upper-left corner.

X does not guarantee to preserve the contents of windows.
When part or all of a window is hidden and then brought back onto the screen,
its contents may be lost.
The server then sends the client program an
Expose
event to notify it that part or all of the window needs to be repainted.
Programs must be prepared to regenerate the contents of windows on demand.

X also provides off-screen storage of graphics objects,
called pixmaps.
Single plane (depth 1) pixmaps are sometimes referred to as
bitmaps.
Pixmaps can be used in most graphics functions interchangeably with
windows and are used in various graphics operations to define patterns or tiles.
Windows and pixmaps together are referred to as drawables.

Most of the functions in Xlib just add requests to an output buffer.
These requests later execute asynchronously on the X server.
Functions that return values of information stored in
the server do not return (that is, they block)
until an explicit reply is received or an error occurs.
You can provide an error handler,
which will be called when the error is reported.

If a client does not want a request to execute asynchronously,
it can follow the request with a call to
XSync,
which blocks until all previously buffered
asynchronous events have been sent and acted on.
As an important side effect,
the output buffer in Xlib is always flushed by a call to any function
that returns a value from the server or waits for input.

Many Xlib functions will return an integer resource ID,
which allows you to refer to objects stored on the X server.
These can be of type
Window,
Font,
Pixmap,
Colormap,
Cursor,
and
GContext,
as defined in the file
<X11/X.h>.
These resources are created by requests and are destroyed
(or freed) by requests or when connections are closed.
Most of these resources are potentially sharable between
applications, and in fact, windows are manipulated explicitly by
window manager programs.
Fonts and cursors are shared automatically across multiple screens.
Fonts are loaded and unloaded as needed and are shared by multiple clients.
Fonts are often cached in the server.
Xlib provides no support for sharing graphics contexts between applications.

Client programs are informed of events.
Events may either be side effects of a request (for example, restacking windows
generates
Expose
events) or completely asynchronous (for example, from the keyboard).
A client program asks to be informed of events.
Because other applications can send events to your application,
programs must be prepared to handle (or ignore) events of all types.

Input events (for example, a key pressed or the pointer moved)
arrive asynchronously from the server and are queued until they are
requested by an explicit call (for example,
XNextEvent
or
XWindowEvent).
In addition, some library
functions (for example,
XRaiseWindow)
generate
Expose
and
ConfigureRequest
events.
These events also arrive asynchronously, but the client may
wish to explicitly wait for them by calling
XSync
after calling a function that can cause the server to generate events.

Errors

Some functions return
Status,
an integer error indication.
If the function fails, it returns a zero.
If the function returns a status of zero,
it has not updated the return arguments.
Because C does not provide multiple return values,
many functions must return their results by writing into client-passed storage.
By default, errors are handled either by a standard library function
or by one that you provide.
Functions that return pointers to strings return NULL pointers if
the string does not exist.

The X server reports protocol errors at the time that it detects them.
If more than one error could be generated for a given request,
the server can report any of them.

Because Xlib usually does not transmit requests to the server immediately
(that is, it buffers them), errors can be reported much later than they
actually occur.
For debugging purposes, however,
Xlib provides a mechanism for forcing synchronous behavior
(see section 11.8.1).
When synchronization is enabled,
errors are reported as they are generated.

When Xlib detects an error,
it calls an error handler,
which your program can provide.
If you do not provide an error handler,
the error is printed, and your program terminates.

Standard Header Files

The following include files are part of the Xlib standard:

<X11/Xlib.h>

This is the main header file for Xlib.
The majority of all Xlib symbols are declared by including this file.
This file also contains the preprocessor symbol
XlibSpecificationRelease.
This symbol is defined to have the 6 in this release of the standard.
(Release 5 of Xlib was the first release to have this symbol.)

<X11/X.h>

This file declares types and constants for the X protocol that are
to be used by applications. It is included automatically from
<X11/Xlib.h>
so application code should never need to
reference this file directly.

<X11/Xcms.h>

This file contains symbols for much of the color management facilities
described in chapter 6.
All functions, types, and symbols with the prefix "Xcms",
plus the Color Conversion Contexts macros, are declared in this file.
<X11/Xlib.h>
must be included before including this file.

<X11/Xutil.h>

This file declares various functions, types, and symbols used for
inter-client communication and application utility functions,
which are described in chapters
14 and
16.
<X11/Xlib.h> must be included before including this file.

<X11/Xresource.h>

This file declares all functions, types, and symbols for the
resource manager facilities, which are described in
chapter 15.
<X11/Xlib.h>
must be included before including this file.

<X11/Xatom.h>

This file declares all predefined atoms,
which are symbols with the prefix "XA_".

<X11/cursorfont.h>

This file declares the cursor symbols for the standard cursor font,
which are listed in Appendix B.
All cursor symbols have the prefix "XC_".

<X11/keysymdef.h>

This file declares all standard KeySym values,
which are symbols with the prefix "XK_".
The KeySyms are arranged in groups, and a preprocessor symbol controls
inclusion of each group. The preprocessor symbol must be defined
prior to inclusion of the file to obtain the associated values.
The preprocessor symbols are
XK_MISCELLANY,
XK_XKB_KEYS,
XK_3270,
XK_LATIN1,
XK_LATIN2,
XK_LATIN3,
XK_LATIN4,
XK_KATAKANA,
XK_ARABIC,
XK_CYRILLIC,
XK_GREEK,
XK_TECHNICAL,
XK_SPECIAL,
XK_PUBLISHING,
XK_APL,
XK_HEBREW,
XK_THAI, and
XK_KOREAN.

<X11/keysym.h>

This file defines the preprocessor symbols
XK_MISCELLANY,
XK_XKB_KEYS,
XK_LATIN1,
XK_LATIN2,
XK_LATIN3,
XK_LATIN4, and
XK_GREEK
and then includes <X11/keysymdef.h>.

<X11/Xlibint.h>

This file declares all the functions, types, and symbols used for
extensions, which are described in Appendix C.
This file automatically includes
<X11/Xlib.h>.

<X11/Xproto.h>

This file declares types and symbols for the basic X protocol,
for use in implementing extensions.
It is included automatically from
<X11/Xlibint.h>,
so application and extension code should never need to
reference this file directly.

<X11/Xprotostr.h>

This file declares types and symbols for the basic X protocol,
for use in implementing extensions.
It is included automatically from
<X11/Xproto.h>,
so application and extension code should never need to
reference this file directly.

<X11/X10.h>

This file declares all the functions, types, and symbols used for the
X10 compatibility functions, which are described in
Appendix D.

Generic Values and Types

The following symbols are defined by Xlib and used throughout the manual:

Xlib defines the type
Bool
and the Boolean values
True
and
False.

None
is the universal null resource ID or atom.

The type
XID
is used for generic resource IDs.

The type XPointer is defined to be char *
and is used as a generic opaque pointer to data.

Naming and Argument Conventions within Xlib

Xlib follows a number of conventions for the naming and syntax of the functions.
Given that you remember what information the function requires,
these conventions are intended to make the syntax of the functions more
predictable.

The major naming conventions are:

To differentiate the X symbols from the other symbols,
the library uses mixed case for external symbols.
It leaves lowercase for variables and all uppercase for user macros,
as per existing convention.

All Xlib functions begin with a capital X.

The beginnings of all function names and symbols are capitalized.

All user-visible data structures begin with a capital X.
More generally,
anything that a user might dereference begins with a capital X.

Macros and other symbols do not begin with a capital X.
To distinguish them from all user symbols,
each word in the macro is capitalized.

All elements of or variables in a data structure are in lowercase.
Compound words, where needed, are constructed with underscores (_).

The display argument, where used, is always first in the argument list.

All resource objects, where used, occur at the beginning of the argument list
immediately after the display argument.

When a graphics context is present together with
another type of resource (most commonly, a drawable), the
graphics context occurs in the argument list after the other
resource.
Drawables outrank all other resources.

The width argument always precedes the height argument in the argument list.

Where the x, y, width, and height arguments are used together,
the x and y arguments always precede the width and height arguments.

Where a mask is accompanied with a structure,
the mask always precedes the pointer to the structure in the argument list.

Programming Considerations

The major programming considerations are:

Coordinates and sizes in X are actually 16-bit quantities.
This decision was made to minimize the bandwidth required for a
given level of performance.
Coordinates usually are declared as an
int
in the interface.
Values larger than 16 bits are truncated silently.
Sizes (width and height) are declared as unsigned quantities.

Keyboards are the greatest variable between different
manufacturers' workstations.
If you want your program to be portable,
you should be particularly conservative here.

Many display systems have limited amounts of off-screen memory.
If you can, you should minimize use of pixmaps and backing
store.

The user should have control of his screen real estate.
Therefore, you should write your applications to react to window management
rather than presume control of the entire screen.
What you do inside of your top-level window, however,
is up to your application.
For further information,
see chapter 14
and the Inter-Client Communication Conventions Manual.

Character Sets and Encodings

Some of the Xlib functions make reference to specific character sets
and character encodings.
The following are the most common:

X Portable Character Set

A basic set of 97 characters,
which are assumed to exist in all locales supported by Xlib.
This set contains the following characters:

This set is the left/lower half
of the graphic character set of ISO8859-1 plus space, tab, and newline.
It is also the set of graphic characters in 7-bit ASCII plus the same
three control characters.
The actual encoding of these characters on the host is system dependent.

Host Portable Character Encoding

The encoding of the X Portable Character Set on the host.
The encoding itself is not defined by this standard,
but the encoding must be the same in all locales supported by Xlib on the host.
If a string is said to be in the Host Portable Character Encoding,
then it only contains characters from the X Portable Character Set,
in the host encoding.

Latin-1

The coded character set defined by the ISO8859-1 standard.

Latin Portable Character Encoding

The encoding of the X Portable Character Set using the Latin-1 codepoints
plus ASCII control characters.
If a string is said to be in the Latin Portable Character Encoding,
then it only contains characters from the X Portable Character Set,
not all of Latin-1.

STRING Encoding

Latin-1, plus tab and newline.

POSIX Portable Filename Character Set

The set of 65 characters,
which can be used in naming files on a POSIX-compliant host,
that are correctly processed in all locales.
The set is:

a..z A..Z 0..9 ._-

Formatting Conventions

Xlib − C Language X Interface uses the
following conventions:

Global symbols are printed in
thisspecialfont.
These can be either function names,
symbols defined in include files, or structure names.
When declared and defined,
function arguments are printed in italics.
In the explanatory text that follows,
they usually are printed in regular type.

Each function is introduced by a general discussion that
distinguishes it from other functions.
The function declaration itself follows,
and each argument is specifically explained.
Although ANSI C function prototype syntax is not used,
Xlib header files normally declare functions using function prototypes
in ANSI C environments.
General discussion of the function, if any is required,
follows the arguments.
Where applicable,
the last paragraph of the explanation lists the possible
Xlib error codes that the function can generate.
For a complete discussion of the Xlib error codes,
see section 11.8.2.

To eliminate any ambiguity between those arguments that you pass and those that
a function returns to you,
the explanations for all arguments that you pass start with the word
specifies or, in the case of multiple arguments, the word specify.
The explanations for all arguments that are returned to you start with the
word returns or, in the case of multiple arguments, the word return.
The explanations for all arguments that you can pass and are returned start
with the words specifies and returns.

Any pointer to a structure that is used to return a value is designated as
such by the _return suffix as part of its name.
All other pointers passed to these functions are
used for reading only.
A few arguments use pointers to structures that are used for
both input and output and are indicated by using the _in_out suffix.

Before your program can use a display, you must establish a connection
to the X server.
Once you have established a connection,
you then can use the Xlib macros and functions discussed in this chapter
to return information about the display.
This chapter discusses how to:

Open (connect to) the display

Obtain information about the display, image formats, or screens

Generate a
NoOperation
protocol request

Free client-created data

Close (disconnect from) a display

Use X Server connection close operations

Use Xlib with threads

Use internal connections

Opening the Display

To open a connection to the X server that controls a display, use
XOpenDisplay.

Display *XOpenDisplay(char *display_name);

display_name

Specifies the hardware display name, which determines the display
and communications domain to be used.
On a POSIX-conformant system, if the display_name is NULL,
it defaults to the value of the DISPLAY environment variable.

The encoding and interpretation of the display name are
implementation-dependent.
Strings in the Host Portable Character Encoding are supported;
support for other characters is implementation-dependent.
On POSIX-conformant systems,
the display name or DISPLAY environment variable can be a string in the format:

protocol/hostname:number.screen_number

protocol

Specifies a protocol family or an alias for a protocol family. Supported
protocol families are implementation dependent. The protocol entry is
optional. If protocol is not specified, the / separating protocol and
hostname must also not be specified.

hostname

Specifies the name of the host machine on which the display is physically
attached.
You follow the hostname with either a single colon (:) or a double colon (::).

number

Specifies the number of the display server on that host machine.
You may optionally follow this display number with a period (.).
A single CPU can have more than one display.
Multiple displays are usually numbered starting with zero.

screen_number

Specifies the screen to be used on that server.
Multiple screens can be controlled by a single X server.
The screen_number sets an internal variable that can be accessed by
using the
DefaultScreen
macro or the
XDefaultScreen
function if you are using languages other than C
(see section 2.2.1).

For example, the following would specify screen 1 of display 0 on the
machine named “dual-headed”:

dual-headed:0.1

The
XOpenDisplay
function returns a
Display
structure that serves as the
connection to the X server and that contains all the information
about that X server.
XOpenDisplay
connects your application to the X server through TCP
or DECnet communications protocols,
or through some local inter-process communication protocol.
If the protocol is specified as "tcp", "inet", or "inet6", or
if no protocol is specified and the hostname is a host machine name and a single colon (:)
separates the hostname and display number,
XOpenDisplay
connects using TCP streams. (If the protocol is specified as "inet", TCP over
IPv4 is used. If the protocol is specified as "inet6", TCP over IPv6 is used.
Otherwise, the implementation determines which IP version is used.)
If the hostname and protocol are both not specified,
Xlib uses whatever it believes is the fastest transport.
If the hostname is a host machine name and a double colon (::)
separates the hostname and display number,
XOpenDisplay
connects using DECnet.
A single X server can support any or all of these transport mechanisms
simultaneously.
A particular Xlib implementation can support many more of these transport
mechanisms.

If successful,
XOpenDisplay
returns a pointer to a
Display
structure,
which is defined in
<X11/Xlib.h>.
If
XOpenDisplay
does not succeed, it returns NULL.
After a successful call to
XOpenDisplay,
all of the screens in the display can be used by the client.
The screen number specified in the display_name argument is returned
by the
DefaultScreen
macro (or the
XDefaultScreen
function).
You can access elements of the
Display
and
Screen
structures only by using the information macros or functions.
For information about using macros and functions to obtain information from
the
Display
structure,
see section 2.2.1.

X servers may implement various types of access control mechanisms
(see section 9.8).

Obtaining Information about the Display, Image Formats, or Screens

The Xlib library provides a number of useful macros
and corresponding functions that return data from the
Display
structure.
The macros are used for C programming,
and their corresponding function equivalents are for other language bindings.
This section discusses the:

Display macros

Image format functions and macros

Screen information macros

All other members of the
Display
structure (that is, those for which no macros are defined) are private to Xlib
and must not be used.
Applications must never directly modify or inspect these private members of the
Display
structure.
The
XDisplayWidth,
XDisplayHeight,
XDisplayCells,
XDisplayPlanes,
XDisplayWidthMM,
and
XDisplayHeightMM
functions in the next sections are misnamed.
These functions really should be named Screenwhatever
and XScreenwhatever, not Displaywhatever or XDisplaywhatever.
Our apologies for the resulting confusion.

Display Macros

Applications should not directly modify any part of the
Display
and
Screen
structures.
The members should be considered read-only,
although they may change as the result of other operations on the display.

The following lists the C language macros,
their corresponding function equivalents that are for other language bindings,
and what data both can return.

AllPlanes()

XAllPlanes()

Both return a value with all bits set to 1 suitable for use in a plane argument to
a procedure.

Both
BlackPixel
and
WhitePixel
can be used in implementing a monochrome application.
These pixel values are for permanently allocated entries in the default
colormap.
The actual RGB (red, green, and blue) values are settable on some screens
and, in any case, may not actually be black or white.
The names are intended to convey the expected relative intensity of the colors.

BlackPixel(display, screen_number)

unsigned long XBlackPixel(Display *display, int screen_number);

display

Specifies the connection to the X server.

screen_number

Specifies the appropriate screen number on the host server.

Both return the black pixel value for the specified screen.

WhitePixel(display, screen_number)

unsigned long XWhitePixel(Display *display, int screen_number);

display

Specifies the connection to the X server.

screen_number

Specifies the appropriate screen number on the host server.

Both return the white pixel value for the specified screen.

ConnectionNumber(display)

int XConnectionNumber(Display *display);

display

Specifies the connection to the X server.

Both return a connection number for the specified display.
On a POSIX-conformant system,
this is the file descriptor of the connection.

DefaultColormap(display, screen_number)

Colormap XDefaultColormap(Display *display, int screen_number);

display

Specifies the connection to the X server.

screen_number

Specifies the appropriate screen number on the host server.

Both return the default colormap ID for allocation on the specified screen.
Most routine allocations of color should be made out of this colormap.

DefaultDepth(display, screen_number)

int XDefaultDepth(Display *display, int screen_number);

display

Specifies the connection to the X server.

screen_number

Specifies the appropriate screen number on the host server.

Both return the depth (number of planes) of the default root window for the
specified screen.
Other depths may also be supported on this screen (see
XMatchVisualInfo).

To determine the number of depths that are available on a given screen, use
XListDepths.

The
XListDepths
function returns the array of depths
that are available on the specified screen.
If the specified screen_number is valid and sufficient memory for the array
can be allocated,
XListDepths
sets count_return to the number of available depths.
Otherwise, it does not set count_return and returns NULL.
To release the memory allocated for the array of depths, use
.

DefaultGC(display, screen_number)

GC XDefaultGC(Display *display, int screen_number);

display

Specifies the connection to the X server.

screen_number

Specifies the appropriate screen number on the host server.

Both return the default graphics context for the root window of the
specified screen.
This GC is created for the convenience of simple applications
and contains the default GC components with the foreground and
background pixel values initialized to the black and white
pixels for the screen, respectively.
You can modify its contents freely because it is not used in any Xlib
function.
This GC should never be freed.

DefaultRootWindow(display)

Window XDefaultRootWindow(Display *display);

display

Specifies the connection to the X server.

Both return the root window for the default screen.

DefaultScreenOfDisplay(display)

Screen *XDefaultScreenOfDisplay(Display *display);

display

Specifies the connection to the X server.

Both return a pointer to the default screen.

ScreenOfDisplay(display, screen_number)

Screen *XScreenOfDisplay(Display *display, int screen_number);

display

Specifies the connection to the X server.

screen_number

Specifies the appropriate screen number on the host server.

Both return a pointer to the indicated screen.

DefaultScreen(display)

int XDefaultScreen(Display *display);

display

Specifies the connection to the X server.

Both return the default screen number referenced by the
XOpenDisplay
function.
This macro or function should be used to retrieve the screen number
in applications that will use only a single screen.

DefaultVisual(display, screen_number)

Visual *XDefaultVisual(Display *display, int screen_number);

display

Specifies the connection to the X server.

screen_number

Specifies the appropriate screen number on the host server.

Both return the default visual type for the specified screen.
For further information about visual types,
see section 3.1.

DisplayCells(display, screen_number)

int XDisplayCells(Display *display, int screen_number);

display

Specifies the connection to the X server.

screen_number

Specifies the appropriate screen number on the host server.

Both return the number of entries in the default colormap.

DisplayPlanes(display, screen_number)

int XDisplayPlanes(Display *display, int screen_number);

display

Specifies the connection to the X server.

screen_number

Specifies the appropriate screen number on the host server.

Both return the depth of the root window of the specified screen.
For an explanation of depth,
see the glossary.

DisplayString(display)

char *XDisplayString(Display *display);

display

Specifies the connection to the X server.

Both return the string that was passed to
XOpenDisplay
when the current display was opened.
On POSIX-conformant systems,
if the passed string was NULL, these return the value of
the DISPLAY environment variable when the current display was opened.
These are useful to applications that invoke the
fork
system call and want to open a new connection to the same display from the
child process as well as for printing error messages.

The
XMaxRequestSize
function returns the maximum request size (in 4-byte units) supported
by the server without using an extended-length protocol encoding.
Single protocol requests to the server can be no larger than this size
unless an extended-length protocol encoding is supported by the server.
The protocol guarantees the size to be no smaller than 4096 units
(16384 bytes).
Xlib automatically breaks data up into multiple protocol requests
as necessary for the following functions:
XDrawPoints,
XDrawRectangles,
XDrawSegments,
XFillArcs,
XFillRectangles,
and
XPutImage.

LastKnownRequestProcessed(display)

unsigned long XLastKnownRequestProcessed(Display *display);

display

Specifies the connection to the X server.

Both extract the full serial number of the last request known by Xlib
to have been processed by the X server.
Xlib automatically sets this number when replies, events, and errors
are received.

NextRequest(display)

unsigned long XNextRequest(Display *display);

display

Specifies the connection to the X server.

Both extract the full serial number that is to be used for the next
request.
Serial numbers are maintained separately for each display connection.

ProtocolVersion(display)

int XProtocolVersion(Display *display);

display

Specifies the connection to the X server.

Both return the major version number (11) of the X protocol associated with
the connected display.

ProtocolRevision(display)

int XProtocolRevision(Display *display);

display

Specifies the connection to the X server.

Both return the minor protocol revision number of the X server.

QLength(display)

int XQLength(Display *display);

display

Specifies the connection to the X server.

Both return the length of the event queue for the connected display.
Note that there may be more events that have not been read into
the queue yet (see
XEventsQueued).

RootWindow(display, screen_number)

Window XRootWindow(Display *display, int screen_number);

display

Specifies the connection to the X server.

screen_number

Specifies the appropriate screen number on the host server.

Both return the root window.
These are useful with functions that need a drawable of a particular screen
and for creating top-level windows.

ScreenCount(display)

int XScreenCount(Display *display);

display

Specifies the connection to the X server.

Both return the number of available screens.

ServerVendor(display)

char *XServerVendor(Display *display);

display

Specifies the connection to the X server.

Both return a pointer to a null-terminated string that provides
some identification of the owner of the X server implementation.
If the data returned by the server is in the Latin Portable Character Encoding,
then the string is in the Host Portable Character Encoding.
Otherwise, the contents of the string are implementation-dependent.

VendorRelease(display)

int XVendorRelease(Display *display);

display

Specifies the connection to the X server.

Both return a number related to a vendor's release of the X server.

Image Format Functions and Macros

Applications are required to present data to the X server
in a format that the server demands.
To help simplify applications,
most of the work required to convert the data is provided by Xlib
(see sections
8.7 and
16.8).

The
XPixmapFormatValues
structure provides an interface to the pixmap format information
that is returned at the time of a connection setup.
It contains:

To obtain the pixmap format information for a given display, use
XListPixmapFormats.

ImageByteOrder(display)

int XImageByteOrder(Display *display, int *count_return);

display

Specifies the connection to the X server.

count_return

Returns the number of (Cn.

The
XListPixmapFormats
function returns an array of
XPixmapFormatValues
structures that describe the types of Z format images supported
by the specified display.
If insufficient memory is available,
XListPixmapFormats
returns NULL.
To free the allocated storage for the
XPixmapFormatValues
structures, use
.

The following lists the C language macros,
their corresponding function equivalents that are for other language bindings,
and what data they both return for the specified server and screen.
These are often used by toolkits as well as by simple applications.

ImageByteOrder(display)

int XImageByteOrder(Display *display);

display

Specifies the connection to the X server.

Both specify the required byte order for images for each scanline unit in
XY format (bitmap) or for each pixel value in
Z format.
The macro or function can return either
LSBFirst
or
MSBFirst.

BitmapUnit(display)

int XBitmapUnit(Display *display);

display

Specifies the connection to the X server.

Both return the size of a bitmap's scanline unit in bits.
The scanline is calculated in multiples of this value.

BitmapBitOrder(display)

int XBitmapBitOrder(Display *display);

display

Specifies the connection to the X server.

Within each bitmap unit, the left-most bit in the bitmap as displayed
on the screen is either the least significant or most significant bit in the
unit.
This macro or function can return
LSBFirst
or
MSBFirst.

BitmapPad(display)

int XBitmapPad(Display *display);

display

Specifies the connection to the X server.

Each scanline must be padded to a multiple of bits returned
by this macro or function.

DisplayHeight(display, screen_number)

int XDisplayHeight(Display *display, int screen_number);

display

Specifies the connection to the X server.

screen_number

Specifies the appropriate screen number on the host server.

Both return an integer that describes the height of the screen
in pixels.

DisplayHeightMM(display, screen_number)

int XDisplayHeightMM(Display *display, int screen_number);

display

Specifies the connection to the X server.

screen_number

Specifies the appropriate screen number on the host server.

Both return the height of the specified screen in millimeters.

DisplayWidth(display, screen_number)

int XDisplayWidth(Display *display, int screen_number);

display

Specifies the connection to the X server.

screen_number

Specifies the appropriate screen number on the host server.

Both return the width of the screen in pixels.

DisplayWidthMM(display, screen_number)

int XDisplayWidthMM(Display *display, int screen_number);

display

Specifies the connection to the X server.

screen_number

Specifies the appropriate screen number on the host server.

Both return the width of the specified screen in millimeters.

Screen Information Macros

The following lists the C language macros,
their corresponding function equivalents that are for other language bindings,
and what data they both can return.
These macros or functions all take a pointer to the appropriate screen
structure.

BlackPixelOfScreen(screen)

unsigned long XBlackPixelOfScreen(Screen *screen);

screen

Specifies the appropriate
Screen
structure.

Both return the black pixel value of the specified screen.

WhitePixelOfScreen(screen)

unsigned long XWhitePixelOfScreen(Screen *screen);

screen

Specifies the appropriate
Screen
structure.

Both return the white pixel value of the specified screen.

CellsOfScreen(screen)

int XCellsOfScreen(Screen *screen);

screen

Specifies the appropriate
Screen
structure.

Both return the number of colormap cells in the default colormap
of the specified screen.

DefaultColormapOfScreen(screen)

Colormap XDefaultColormapOfScreen(Screen *screen);

screen

Specifies the appropriate
Screen
structure.

Both return the default colormap of the specified screen.

DefaultDepthOfScreen(screen)

int XDefaultDepthOfScreen(Screen *screen);

screen

Specifies the appropriate
Screen
structure.

Both return the depth of the root window.

DefaultGCOfScreen(screen)

GC XDefaultGCOfScreen(Screen *screen);

screen

Specifies the appropriate
Screen
structure.

Both return a default graphics context (GC) of the specified screen,
which has the same depth as the root window of the screen.
The GC must never be freed.

DefaultVisualOfScreen(screen)

Visual *XDefaultVisualOfScreen(Screen *screen);

screen

Specifies the appropriate
Screen
structure.

Both return the default visual of the specified screen.
For information on visual types,
see section 3.1.

DoesBackingStore(screen)

int XDoesBackingStore(Screen *screen);

screen

Specifies the appropriate
Screen
structure.

Both return a value indicating whether the screen supports backing
stores.
The value returned can be one of
WhenMapped,
NotUseful,
or
Always
(see section 3.2.4).

DoesSaveUnders(screen)

Bool XDoesSaveUnders(Screen *screen);

screen

Specifies the appropriate
Screen
structure.

Both return a Boolean value indicating whether the
screen supports save unders.
If
True,
the screen supports save unders.
If
False,
the screen does not support save unders
(see section 3.2.5).

DisplayOfScreen(screen)

Display *XDisplayOfScreen(Screen *screen);

screen

Specifies the appropriate
Screen
structure.

Both return the display of the specified screen.

EventMaskOfScreen(screen)

long XEventMaskOfScreen(Screen *screen);

screen

Specifies the appropriate
Screen
structure.

The
XScreenNumberOfScreen
function returns the screen index number of the specified screen.

EventMaskOfScreen(screen)

long XEventMaskOfScreen(Screen *screen);

screen

Specifies the appropriate
Screen
structure.

Both return the event mask of the root window for the specified screen
at connection setup time.

WidthOfScreen(screen)

int XWidthOfScreen(Screen *screen);

screen

Specifies the appropriate
Screen
structure.

Both return the width of the specified screen in pixels.

HeightOfScreen(screen)

int XHeightOfScreen(Screen *screen);

screen

Specifies the appropriate
Screen
structure.

Both return the height of the specified screen in pixels.

WidthMMOfScreen(screen)

int XWidthMMOfScreen(Screen *screen);

screen

Specifies the appropriate
Screen
structure.

Both return the width of the specified screen in millimeters.

HeightMMOfScreen(screen)

int XHeightMMOfScreen(Screen *screen);

screen

Specifies the appropriate
Screen
structure.

Both return the height of the specified screen in millimeters.

MaxCmapsOfScreen(screen)

int XMaxCmapsOfScreen(Screen *screen);

screen

Specifies the appropriate
Screen
structure.

Both return the maximum number of installed colormaps supported
by the specified screen
(see section 9.3).

MinCmapsOfScreen(screen)

int XMinCmapsOfScreen(Screen *screen);

screen

Specifies the appropriate
Screen
structure.

Both return the minimum number of installed colormaps supported
by the specified screen
(see section 9.3).

Generating a NoOperation Protocol Request

The
XNoOp
function sends a
NoOperation
protocol request to the X server,
thereby exercising the connection.

Freeing Client-Created Data

To free in-memory data that was created by an Xlib function, use
.

XFree(void *data);

data

Specifies the data that is to be freed.

The
function is a general-purpose Xlib routine that frees the specified data.
You must use it to free any objects that were allocated by Xlib,
unless an alternate function is explicitly specified for the object.
A NULL pointer cannot be passed to this function.

Closing the Display

To close a display or disconnect from the X server, use
XCloseDisplay.

XCloseDisplay(Display *display);

display

Specifies the connection to the X server.

The
XCloseDisplay
function closes the connection to the X server for the display specified in the
Display
structure and destroys all windows, resource IDs
(Window,
Font,
Pixmap,
Colormap,
Cursor,
and
GContext),
or other resources that the client has created
on this display, unless the close-down mode of the resource has been changed
(see
).
Therefore, these windows, resource IDs, and other resources should never be
referenced again or an error will be generated.
Before exiting, you should call
XCloseDisplay
explicitly so that any pending errors are reported as
XCloseDisplay
performs a final
XSync
operation.

XCloseDisplay
can generate a
BadGC
error.

Xlib provides a function to permit the resources owned by a client
to survive after the client's connection is closed.
To change a client's close-down mode, use
.

XSetCloseDownMode(Display *display, int close_mode);

display

Specifies the connection to the X server.

close_mode

Specifies the client close-down mode.
You can pass
DestroyAll,
RetainPermanent,
or
RetainTemporary.

The
defines what will happen to the client's resources at connection close.
A connection starts in
DestroyAll
mode.
For information on what happens to the client's resources when the
close_mode argument is
RetainPermanent
or
RetainTemporary,
see section 2.6.

can generate a
BadValue
error.

Using X Server Connection Close Operations

When the X server's connection to a client is closed
either by an explicit call to
XCloseDisplay
or by a process that exits, the X server performs the following
automatic operations:

It marks all resources (including colormap entries) allocated
by the client either as permanent or temporary,
depending on whether the close-down mode is
RetainPermanent
or
RetainTemporary.
However, this does not prevent other client applications from explicitly
destroying the resources (see
).

When the close-down mode is
DestroyAll,
the X server destroys all of a client's resources as follows:

It examines each window in the client's save-set to determine if it is an inferior
(subwindow) of a window created by the client.
(The save-set is a list of other clients' windows
that are referred to as save-set windows.)
If so, the X server reparents the save-set window to the closest ancestor so
that the save-set window is not an inferior of a window created by the client.
The reparenting leaves unchanged the absolute coordinates (with respect to
the root window) of the upper-left outer corner of the save-set
window.

It performs a
MapWindow
request on the save-set window if the save-set window is unmapped.
The X server does this even if the save-set window was not an inferior of
a window created by the client.

It destroys all windows created by the client.

It performs the appropriate free request on each nonwindow resource created by
the client in the server (for example,
Font,
Pixmap,
Cursor,
Colormap,
and
GContext).

It frees all colors and colormap entries allocated by a client application.

Additional processing occurs when the last connection to the X server closes.
An X server goes through a cycle of having no connections and having some
connections.
When the last connection to the X server closes as a result of a connection
closing with the close_mode of
DestroyAll,
the X server does the following:

It resets its state as if it had just been
started.
The X server begins by destroying all lingering resources from
clients that have terminated in
RetainPermanent
or
RetainTemporary
mode.

It resets all device maps and attributes
(for example, key click, bell volume, and acceleration)
as well as the access control list.

It restores the standard root tiles and cursors.

It restores the default font path.

It restores the input focus to state
PointerRoot.

However, the X server does not reset if you close a connection with a close-down
mode set to
RetainPermanent
or
RetainTemporary.

Using Xlib with Threads

On systems that have threads, support may be provided to permit
multiple threads to use Xlib concurrently.

To initialize support for concurrent threads, use
XInitThreads.

Status XInitThreads();

The
XInitThreads
function initializes Xlib support for concurrent threads.
This function must be the first Xlib function a
multi-threaded program calls, and it must complete
before any other Xlib call is made.
This function returns a nonzero status if initialization was
successful; otherwise, it returns zero.
On systems that do not support threads, this function always returns zero.

It is only necessary to call this function if multiple threads
might use Xlib concurrently. If all calls to Xlib functions
are protected by some other access mechanism (for example,
a mutual exclusion lock in a toolkit or through explicit client
programming), Xlib thread initialization is not required.
It is recommended that single-threaded programs not call this function.

To lock a display across several Xlib calls, use
XLockDisplay.

XLockDisplay(Display *display);

display

Specifies the connection to the X server.

The
XLockDisplay
function locks out all other threads from using the specified display.
Other threads attempting to use the display will block until
the display is unlocked by this thread.
Nested calls to
XLockDisplay
work correctly; the display will not actually be unlocked until
has been called the same number of times as
XLockDisplay.
This function has no effect unless Xlib was successfully initialized
for threads using
XInitThreads.

To unlock a display, use
.

XUnlockDisplay(Display *display);

display

Specifies the connection to the X server.

The
function allows other threads to use the specified display again.
Any threads that have blocked on the display are allowed to continue.
Nested locking works correctly; if
XLockDisplay
has been called multiple times by a thread, then
must be called an equal number of times before the display is
actually unlocked.
This function has no effect unless Xlib was successfully initialized
for threads using
XInitThreads.

Using Internal Connections

In addition to the connection to the X server, an Xlib implementation
may require connections to other kinds of servers (for example, to
input method servers as described in
chapter 13).
Toolkits and clients
that use multiple displays, or that use displays in combination with
other inputs, need to obtain these additional connections to correctly
block until input is available and need to process that input
when it is available. Simple clients that use a single display and
block for input in an Xlib event function do not need to use these
facilities.

The
function registers a procedure to be called each time Xlib opens or closes an
internal connection for the specified display. The procedure is passed the
display, the specified client_data, the file descriptor for the connection,
a Boolean indicating whether the connection is being opened or closed, and a
pointer to a location for private watch data. If opening is
True,
the procedure can store a pointer to private data in the location pointed
to by watch_data;
when the procedure is later called for this same connection and opening is
False,
the location pointed to by watch_data will hold this same private data pointer.

This function can be called at any time after a display is opened.
If internal connections already exist, the registered procedure will
immediately be called for each of them, before
returns.
returns a nonzero status if the procedure is successfully registered;
otherwise, it returns zero.

The registered procedure should not call any Xlib functions.
If the procedure directly or indirectly causes the state of internal
connections or watch procedures to change, the result is not defined.
If Xlib has been initialized for threads, the procedure is called with
the display locked and the result of a call by the procedure to any
Xlib function that locks the display is not defined unless the executing
thread has externally locked the display using
XLockDisplay.

To stop tracking internal connections for a display, use
XRemoveConnectionWatch.

The
XProcessInternalConnection
function processes input available on an internal connection.
This function should be called for an internal connection only
after an operating system facility (for example,
select
or
poll)
has indicated that input is available; otherwise,
the effect is not defined.

The
XInternalConnectionNumbers
function returns a list of the file descriptors for all internal
connections currently open for the specified display.
When the allocated list is no longer needed,
free it by using
.
This functions returns a nonzero status if the list is successfully allocated;
otherwise, it returns zero.

Visual Types

On some display hardware,
it may be possible to deal with color resources in more than one way.
For example, you may be able to deal with a screen of either 12-bit depth
with arbitrary mapping of pixel to color (pseudo-color) or 24-bit depth
with 8 bits of the pixel dedicated to each of red, green, and blue.
These different ways of dealing with the visual aspects of the screen
are called visuals.
For each screen of the display, there may be a list of valid visual types
supported at different depths of the screen.
Because default windows and visual types are defined for each screen,
most simple applications need not deal with this complexity.
Xlib provides macros and functions that return the default root window,
the default depth of the default root window, and the default visual type
(see sections 2.2.1
and 16.7).

Xlib uses an opaque
Visual
structure that contains information about the possible color mapping.
The visual utility functions
(see section 16.7)
use an
XVisualInfo
structure to return this information to an application.
The members of this structure pertinent to this discussion are class, red_mask,
green_mask, blue_mask, bits_per_rgb, and colormap_size.
The class member specifies one of the possible visual classes of the screen
and can be
StaticGray,
StaticColor,
TrueColor,
GrayScale,
PseudoColor,
or
DirectColor.

The following concepts may serve to make the explanation of
visual types clearer.
The screen can be color or grayscale,
can have a colormap that is writable or read-only,
and can also have a colormap whose indices are decomposed into separate
RGB pieces, provided one is not on a grayscale screen.
This leads to the following diagram:

Conceptually,
as each pixel is read out of video memory for display on the screen,
it goes through a look-up stage by indexing into a colormap.
Colormaps can be manipulated arbitrarily on some hardware,
in limited ways on other hardware, and not at all on other hardware.
The visual types affect the colormap and
the RGB values in the following ways:

For
PseudoColor,
a pixel value indexes a colormap to produce
independent RGB values, and the RGB values can be changed dynamically.

GrayScale
is treated the same way as
PseudoColor
except that the primary that drives the screen is undefined.
Thus, the client should always store the
same value for red, green, and blue in the colormaps.

For
DirectColor,
a pixel value is decomposed into separate RGB subfields, and each
subfield separately indexes the colormap for the corresponding value.
The RGB values can be changed dynamically.

TrueColor
is treated the same way as
DirectColor
except that the colormap has predefined, read-only RGB values.
These RGB values are server dependent but provide linear or near-linear
ramps in each primary.

StaticColor
is treated the same way as
PseudoColor
except that the colormap has predefined,
read-only, server-dependent RGB values.

StaticGray
is treated the same way as
StaticColor
except that the RGB values are equal for any single pixel
value, thus resulting in shades of gray.
StaticGray
with a two-entry
colormap can be thought of as monochrome.

The red_mask, green_mask, and blue_mask members are only defined for
DirectColor
and
TrueColor.
Each has one contiguous set of bits with no
intersections.
The bits_per_rgb member specifies the log base 2 of the
number of distinct color values (individually) of red, green, and blue.
Actual RGB values are unsigned 16-bit numbers.
The colormap_size member defines the number of available colormap entries
in a newly created colormap.
For
DirectColor
and
TrueColor,
this is the size of an individual pixel subfield.

Window Attributes

All
InputOutput
windows have a border width of zero or more pixels, an optional background,
an event suppression mask (which suppresses propagation of events from
children), and a property list
(see section 4.3).
The window border and background can be a solid color or a pattern, called
a tile.
All windows except the root have a parent and are clipped by their parent.
If a window is stacked on top of another window, it obscures that other
window for the purpose of input.
If a window has a background (almost all do), it obscures the other
window for purposes of output.
Attempts to output to the obscured area do nothing,
and no input events (for example, pointer motion) are generated for the
obscured area.

Both
InputOutput
and
InputOnly
windows have the following common attributes,
which are the only attributes of an
InputOnly
window:

win-gravity

event-mask

do-not-propagate-mask

override-redirect

cursor

If you specify any other attributes for an
InputOnly
window,
a
BadMatch
error results.

InputOnly
windows are used for controlling input events in situations where
InputOutput
windows are unnecessary.
InputOnly
windows are invisible; can only be used to control such things as
cursors, input event generation, and grabbing;
and cannot be used in any graphics requests.
Note that
InputOnly
windows cannot have
InputOutput
windows as inferiors.

Windows have borders of a programmable width and pattern
as well as a background pattern or tile.
Pixel values can be used for solid colors.
The background and border pixmaps can be destroyed immediately after
creating the window if no further explicit references to them
are to be made.
The pattern can either be relative to the parent
or absolute.
If
ParentRelative,
the parent's background is used.

When windows are first created,
they are not visible (not mapped) on the screen.
Any output to a window that is not visible on the screen
and that does not have backing store will be discarded.
An application may wish to create a window long before it is
mapped to the screen.
When a window is eventually mapped to the screen
(using
XMapWindow),
the X server generates an
Expose
event for the window if backing store has not been maintained.

A window manager can override your choice of size,
border width, and position for a top-level window.
Your program must be prepared to use the actual size and position
of the top window.
It is not acceptable for a client application to resize itself
unless in direct response to a human command to do so.
Instead, either your program should use the space given to it,
or if the space is too small for any useful work, your program
might ask the user to resize the window.
The border of your top-level window is considered fair game
for window managers.

To set an attribute of a window,
set the appropriate member of the
XSetWindowAttributes
structure and OR in the corresponding value bitmask in your subsequent calls to
XCreateWindow
and
XChangeWindowAttributes,
or use one of the other convenience functions that set the appropriate
attribute.
The symbols for the value mask bits and the
XSetWindowAttributes
structure are:

The following lists the defaults for each window attribute and indicates
whether the attribute is applicable to
InputOutput
and
InputOnly
windows:

Attribute

Default

InputOutput

InputOnly

background-pixmap

None

Yes

No

background-pixel

Undefined

Yes

No

border-pixmap

CopyFromParent

Yes

No

border-pixel

Undefined

Yes

No

bit-gravity

ForgetGravity

Yes

No

win-gravity

NorthWestGravity

Yes

Yes

backing-store

NotUseful

Yes

No

backing-planes

All ones

Yes

No

backing-pixel

zero

Yes

No

save-under

False

Yes

No

event-mask

empty set

Yes

Yes

do-not-propagate-mask

empty set

Yes

Yes

override-redirect

False

Yes

Yes

colormap

CopyFromParent

Yes

No

cursor

None

Yes

Yes

Background Attribute

Only
InputOutput
windows can have a background.
You can set the background of an
InputOutput
window by using a pixel or a pixmap.

The background-pixmap attribute of a window specifies the pixmap to be used for
a window's background.
This pixmap can be of any size, although some sizes may be faster than others.
The background-pixel attribute of a window specifies a pixel value used to paint
a window's background in a single color.

You can set the background-pixmap to a pixmap,
None
(default), or
ParentRelative.
You can set the background-pixel of a window to any pixel value (no default).
If you specify a background-pixel,
it overrides either the default background-pixmap
or any value you may have set in the background-pixmap.
A pixmap of an undefined size that is filled with the background-pixel is used
for the background.
Range checking is not performed on the background pixel;
it simply is truncated to the appropriate number of bits.

If you set the background-pixmap,
it overrides the default.
The background-pixmap and the window must have the same depth,
or a
BadMatch
error results.
If you set background-pixmap to
None,
the window has no defined background.
If you set the background-pixmap to
ParentRelative:

The parent window's background-pixmap is used.
The child window, however, must have the same depth as
its parent,
or a
BadMatch
error results.

If the parent window has a background-pixmap of
None,
the window also has a background-pixmap of
None.

A copy of the parent window's background-pixmap is not made.
The parent's background-pixmap is examined each time the child window's
background-pixmap is required.

The background tile origin always aligns with the parent window's
background tile origin.
If the background-pixmap is not
ParentRelative,
the background tile origin is the child window's origin.

Setting a new background, whether by setting background-pixmap or
background-pixel, overrides any previous background.
The background-pixmap can be freed immediately if no further explicit reference
is made to it (the X server will keep a copy to use when needed).
If you later draw into the pixmap used for the background,
what happens is undefined because the
X implementation is free to make a copy of the pixmap or
to use the same pixmap.

When no valid contents are available for regions of a window
and either the regions are visible or the server is maintaining backing store,
the server automatically tiles the regions with the window's background
unless the window has a background of
None.
If the background is
None,
the previous screen contents from other windows of the same depth as the window
are simply left in place as long as the contents come from the parent of the
window or an inferior of the parent.
Otherwise, the initial contents of the exposed regions are undefined.
Expose
events are then generated for the regions, even if the background-pixmap
is
None
(see section 10.9).

Border Attribute

Only
InputOutput
windows can have a border.
You can set the border of an
InputOutput
window by using a pixel or a pixmap.

The border-pixmap attribute of a window specifies the pixmap to be used
for a window's border.
The border-pixel attribute of a window specifies a pixmap of undefined size
filled with that pixel be used for a window's border.
Range checking is not performed on the background pixel;
it simply is truncated to the appropriate number of bits.
The border tile origin is always the same as the background tile origin.

You can also set the border-pixmap to a pixmap of any size (some may be faster
than others) or to
CopyFromParent
(default).
You can set the border-pixel to any pixel value (no default).

If you set a border-pixmap,
it overrides the default.
The border-pixmap and the window must have the same depth,
or a
BadMatch
error results.
If you set the border-pixmap to
CopyFromParent,
the parent window's border-pixmap is copied.
Subsequent changes to the parent window's border attribute do not affect
the child window.
However, the child window must have the same depth as the parent window,
or a
BadMatch
error results.

The border-pixmap can be freed immediately if no further explicit reference
is made to it.
If you later draw into the pixmap used for the border,
what happens is undefined because the
X implementation is free either to make a copy of the pixmap or
to use the same pixmap.
If you specify a border-pixel,
it overrides either the default border-pixmap
or any value you may have set in the border-pixmap.
All pixels in the window's border will be set to the border-pixel.
Setting a new border, whether by setting border-pixel or by setting
border-pixmap, overrides any previous border.

Output to a window is always clipped to the inside of the window.
Therefore, graphics operations never affect the window border.

Gravity Attributes

The bit gravity of a window defines which region of the window should be
retained when an
InputOutput
window is resized.
The default value for the bit-gravity attribute is
ForgetGravity.
The window gravity of a window allows you to define how the
InputOutput
or
InputOnly
window should be repositioned if its parent is resized.
The default value for the win-gravity attribute is
NorthWestGravity.

If the inside width or height of a window is not changed
and if the window is moved or its border is changed,
then the contents of the window are not lost but move with the window.
Changing the inside width or height of the window causes its contents to be
moved or lost (depending on the bit-gravity of the window) and causes
children to be reconfigured (depending on their win-gravity).
For a
change of width and height, the (x, y) pairs are defined:

Gravity Direction

Coordinates

NorthWestGravity

(0, 0)

NorthGravity

(Width/2, 0)

NorthEastGravity

(Width, 0)

WestGravity

(0, Height/2)

CenterGravity

(Width/2, Height/2)

EastGravity

(Width, Height/2)

SouthWestGravity

(0, Height)

SouthGravity

(Width/2, Height)

SouthEastGravity

(Width, Height)

When a window with one of these bit-gravity values is resized,
the corresponding pair
defines the change in position of each pixel in the window.
When a window with one of these win-gravities has its parent window resized,
the corresponding pair defines the change in position of the window
within the parent.
When a window is so repositioned, a
GravityNotify
event is generated
(see section 10.10.5).

A bit-gravity of
StaticGravity
indicates that the contents or origin should not move relative to the
origin of the root window.
If the change in size of the window is coupled with a change in position (x, y),
then for bit-gravity the change in position of each pixel is (−x, −y), and for
win-gravity the change in position of a child when its parent is so resized is
(−x, −y).
Note that
StaticGravity
still only takes effect when the width or height of the window is changed,
not when the window is moved.

A bit-gravity of
ForgetGravity
indicates that the window's contents are always discarded after a size change,
even if a backing store or save under has been requested.
The window is tiled with its background
and zero or more
Expose
events are generated.
If no background is defined, the existing screen contents are not
altered.
Some X servers may also ignore the specified bit-gravity and
always generate
Expose
events.

The contents and borders of inferiors are not affected by their parent's
bit-gravity.
A server is permitted to ignore the specified bit-gravity and use
Forget
instead.

A win-gravity of
UnmapGravity
is like
NorthWestGravity
(the window is not moved),
except the child is also
unmapped when the parent is resized,
and an
UnmapNotify
event is
generated.

Backing Store Attribute

Some implementations of the X server may choose to maintain the contents of
InputOutput
windows.
If the X server maintains the contents of a window,
the off-screen saved pixels
are known as backing store.
The backing store advises the X server on what to do
with the contents of a window.
The backing-store attribute can be set to
NotUseful
(default),
WhenMapped,
or
Always.

A backing-store attribute of
NotUseful
advises the X server that
maintaining contents is unnecessary,
although some X implementations may
still choose to maintain contents and, therefore, not generate
Expose
events.
A backing-store attribute of
WhenMapped
advises the X server that maintaining contents of
obscured regions when the window is mapped would be beneficial.
In this case,
the server may generate an
Expose
event when the window is created.
A backing-store attribute of
Always
advises the X server that maintaining contents even when
the window is unmapped would be beneficial.
Even if the window is larger than its parent,
this is a request to the X server to maintain complete contents,
not just the region within the parent window boundaries.
While the X server maintains the window's contents,
Expose
events normally are not generated,
but the X server may stop maintaining
contents at any time.

When the contents of obscured regions of a window are being maintained,
regions obscured by noninferior windows are included in the destination
of graphics requests (and source, when the window is the source).
However, regions obscured by inferior windows are not included.

Save Under Flag

Some server implementations may preserve contents of
InputOutput
windows under other
InputOutput
windows.
This is not the same as preserving the contents of a window for you.
You may get better visual
appeal if transient windows (for example, pop-up menus) request that the system
preserve the screen contents under them,
so the temporarily obscured applications do not have to repaint.

You can set the save-under flag to
True
or
False
(default).
If save-under is
True,
the X server is advised that, when this window is mapped,
saving the contents of windows it obscures would be beneficial.

Backing Planes and Backing Pixel Attributes

You can set backing planes to indicate (with bits set to 1)
which bit planes of an
InputOutput
window hold dynamic data that must be preserved in backing store
and during save unders.
The default value for the backing-planes attribute is all bits set to 1.
You can set backing pixel to specify what bits to use in planes not
covered by backing planes.
The default value for the backing-pixel attribute is all bits set to 0.
The X server is free to save only the specified bit planes in the backing store
or the save under and is free to regenerate the remaining planes with
the specified pixel value.
Any extraneous bits in these values (that is, those bits beyond
the specified depth of the window) may be simply ignored.
If you request backing store or save unders,
you should use these members to minimize the amount of off-screen memory
required to store your window.

Event Mask and Do Not Propagate Mask Attributes

The event mask defines which events the client is interested in for this
InputOutput
or
InputOnly
window (or, for some event types, inferiors of this window).
The event mask is the bitwise inclusive OR of zero or more of the
valid event mask bits.
You can specify that no maskable events are reported by setting
NoEventMask
(default).

The do-not-propagate-mask attribute
defines which events should not be propagated to
ancestor windows when no client has the event type selected in this
InputOutput
or
InputOnly
window.
The do-not-propagate-mask is the bitwise inclusive OR of zero or more
of the following masks:
KeyPress,
KeyRelease,
ButtonPress,
ButtonRelease,
PointerMotion,
Button1Motion,
Button2Motion,
Button3Motion,
Button4Motion,
Button5Motion,
and
ButtonMotion.
You can specify that all events are propagated by setting
NoEventMask
(default).

Override Redirect Flag

To control window placement or to add decoration,
a window manager often needs to intercept (redirect) any map or configure
request.
Pop-up windows, however, often need to be mapped without a window manager
getting in the way.
To control whether an
InputOutput
or
InputOnly
window is to ignore these structure control facilities,
use the override-redirect flag.

The override-redirect flag specifies whether map and configure requests
on this window should override a
SubstructureRedirectMask
on the parent.
You can set the override-redirect flag to
True
or
False
(default).
Window managers use this information to avoid tampering with pop-up windows
(see also chapter 14).

Colormap Attribute

The colormap attribute specifies which colormap best reflects the true
colors of the
InputOutput
window.
The colormap must have the same visual type as the window,
or a
BadMatch
error results.
X servers capable of supporting multiple
hardware colormaps can use this information,
and window managers can use it for calls to
XInstallColormap.
You can set the colormap attribute to a colormap or to
CopyFromParent
(default).

If you set the colormap to
CopyFromParent,
the parent window's colormap is copied and used by its child.
However, the child window must have the same visual type as the parent,
or a
BadMatch
error results.
The parent window must not have a colormap of
None,
or a
BadMatch
error results.
The colormap is copied by sharing the colormap object between the child
and parent, not by making a complete copy of the colormap contents.
Subsequent changes to the parent window's colormap attribute do
not affect the child window.

Cursor Attribute

The cursor attribute specifies which cursor is to be used when the pointer is
in the
InputOutput
or
InputOnly
window.
You can set the cursor to a cursor or
None
(default).

If you set the cursor to
None,
the parent's cursor is used when the
pointer is in the
InputOutput
or
InputOnly
window, and any change in the parent's cursor will cause an
immediate change in the displayed cursor.
By calling
XFreeCursor,
the cursor can be freed immediately as long as no further explicit reference
to it is made.

Creating Windows

Xlib provides basic ways for creating windows,
and toolkits often supply higher-level functions specifically for
creating and placing top-level windows,
which are discussed in the appropriate toolkit documentation.
If you do not use a toolkit, however,
you must provide some standard information or hints for the window
manager by using the Xlib inter-client communication functions
(see chapter 14).

If you use Xlib to create your own top-level windows
(direct children of the root window),
you must observe the following rules so that all applications interact
reasonably across the different styles of window management:

You must never fight with the window manager for the size or
placement of your top-level window.

You must be able to deal with whatever size window you get,
even if this means that your application just prints a message
like “Please make me bigger” in its window.

You should only attempt to resize or move top-level windows in
direct response to a user request.
If a request to change the size of a top-level window fails,
you must be prepared to live with what you get.
You are free to resize or move the children of top-level
windows as necessary.
(Toolkits often have facilities for automatic relayout.)

If you do not use a toolkit that automatically sets standard window properties,
you should set these properties for top-level windows before mapping them.

XCreateWindow
is the more general function that allows you to set specific window attributes
when you create a window.
XCreateSimpleWindow
creates a window that inherits its attributes from its parent window.

The X server acts as if
InputOnly
windows do not exist for
the purposes of graphics requests, exposure processing, and
VisibilityNotify
events.
An
InputOnly
window cannot be used as a
drawable (that is, as a source or destination for graphics requests).
InputOnly
and
InputOutput
windows act identically in other respects (properties,
grabs, input control, and so on).
Extension packages can define other classes of windows.

To create an unmapped window and set its window attributes, use
XCreateWindow.

Specifies the parent window.
borders and are relative to the inside of the parent window's borders

x

y

Specify the x and y coordinates(Xy.
and do not include the created window's borders

width

height

Specify the width and height(Wh.
The dimensions must be nonzero,
or a
BadValue
error results.

border_width

Specifies the width of the created window's border in pixels.

depth

Specifies the window's depth.
A depth of
CopyFromParent
means the depth is taken from the parent.

class

Specifies the created window's class.
You can pass
InputOutput,
InputOnly,
or
CopyFromParent.
A class of
CopyFromParent
means the class
is taken from the parent.

visual

Specifies the visual type.
A visual of
CopyFromParent
means the visual type is taken from the
parent.

valuemask

Specifies which window attributes are defined in the attributes
argument.
This mask is the bitwise inclusive OR of the valid attribute mask bits.
If valuemask is zero,
the attributes are ignored and are not referenced.

attributes

Specifies the structure from which the values (as specified by the value mask)
are to be taken.
The value mask should have the appropriate bits
set to indicate which attributes have been set in the structure.

The
XCreateWindow
function creates an unmapped subwindow for a specified parent window,
returns the window ID of the created window,
and causes the X server to generate a
CreateNotify
event.
The created window is placed on top in the stacking order
with respect to siblings.

The coordinate system has the X axis horizontal and the Y axis vertical
with the origin [0, 0] at the upper-left corner.
Coordinates are integral,
in terms of pixels,
and coincide with pixel centers.
Each window and pixmap has its own coordinate system.
For a window,
the origin is inside the border at the inside, upper-left corner.

The border_width for an
InputOnly
window must be zero, or a
BadMatch
error results.
For class
InputOutput,
the visual type and depth must be a combination supported for the screen,
or a
BadMatch
error results.
The depth need not be the same as the parent,
but the parent must not be a window of class
InputOnly,
or a
BadMatch
error results.
For an
InputOnly
window,
the depth must be zero, and the visual must be one supported by the screen.
If either condition is not met,
a
BadMatch
error results.
The parent window, however, may have any depth and class.
If you specify any invalid window attribute for a window, a
BadMatch
error results.

The created window is not yet displayed (mapped) on the user's display.
To display the window, call
XMapWindow.
The new window initially uses the same cursor as
its parent.
A new cursor can be defined for the new window by calling
XDefineCursor.
The window will not be visible on the screen unless it and all of its
ancestors are mapped and it is not obscured by any of its ancestors.

Specifies the parent window.
and are relative to the inside of the parent window's borders

x

y

Specify the x and y coordinates(Xy.
and do not include the created window's borders

width

height

Specify the width and height(Wh.
The dimensions must be nonzero,
or a
BadValue
error results.

border_width

Specifies the width of the created window's border in pixels.

border

Specifies the border pixel value of the window.

background

Specifies the background pixel value of the window.

The
XCreateSimpleWindow
function creates an unmapped
InputOutput
subwindow for a specified parent window, returns the
window ID of the created window, and causes the X server to generate a
CreateNotify
event.
The created window is placed on top in the stacking order with respect to
siblings.
Any part of the window that extends outside its parent window is clipped.
The border_width for an
InputOnly
window must be zero, or a
BadMatch
error results.
XCreateSimpleWindow
inherits its depth, class, and visual from its parent.
All other window attributes, except background and border,
have their default values.

The
XDestroyWindow
function destroys the specified window as well as all of its subwindows and causes
the X server to generate a
DestroyNotify
event for each window.
The window should never be referenced again.
If the window specified by the w argument is mapped,
it is unmapped automatically.
The ordering of the
DestroyNotify
events is such that for any given window being destroyed,
DestroyNotify
is generated on any inferiors of the window before being generated on
the window itself.
The ordering among siblings and across subhierarchies is not otherwise
constrained.
If the window you specified is a root window, no windows are destroyed.
Destroying a mapped window will generate
Expose
events on other windows that were obscured by the window being destroyed.

The
XDestroySubwindows
function destroys all inferior windows of the specified window,
in bottom-to-top stacking order.
It causes the X server to generate a
DestroyNotify
event for each window.
If any mapped
subwindows were actually destroyed,
XDestroySubwindows
causes the X server to generate
Expose
events on the specified window.
This is much more efficient than deleting many windows
one at a time because much of the work need be performed only once for all
of the windows, rather than for each window.
The subwindows should never be referenced again.

Mapping Windows

A window is considered mapped if an
XMapWindow
call has been made on it.
It may not be visible on the screen for one of the following reasons:

It is obscured by another opaque window.

One of its ancestors is not mapped.

It is entirely clipped by an ancestor.

Expose
events are generated for the window when part or all of
it becomes visible on the screen.
A client receives the
Expose
events only if it has asked for them.
Windows retain their position in the stacking order when they are unmapped.

A window manager may want to control the placement of subwindows.
If
SubstructureRedirectMask
has been selected by a window manager
on a parent window (usually a root window),
a map request initiated by other clients on a child window is not performed,
and the window manager is sent a
MapRequest
event.
However, if the override-redirect flag on the child had been set to
True
(usually only on pop-up menus),
the map request is performed.

A tiling window manager might decide to reposition and resize other clients'
windows and then decide to map the window to its final location.
A window manager that wants to provide decoration might
reparent the child into a frame first.
For further information,
see sections 3.2.8
and 10.10.
Only a single client at a time can select for
SubstructureRedirectMask.

Similarly, a single client can select for
ResizeRedirectMask
on a parent window.
Then, any attempt to resize the window by another client is suppressed, and
the client receives a
ResizeRequest
event.

The
XMapWindow
function
maps the window and all of its
subwindows that have had map requests.
Mapping a window that has an unmapped ancestor does not display the
window but marks it as eligible for display when the ancestor becomes
mapped.
Such a window is called unviewable.
When all its ancestors are mapped,
the window becomes viewable
and will be visible on the screen if it is not obscured by another window.
This function has no effect if the window is already mapped.

If the override-redirect of the window is
False
and if some other client has selected
SubstructureRedirectMask
on the parent window, then the X server generates a
MapRequest
event, and the
XMapWindow
function does not map the window.
Otherwise, the window is mapped, and the X server generates a
MapNotify
event.

If the window becomes viewable and no earlier contents for it are remembered,
the X server tiles the window with its background.
If the window's background is undefined,
the existing screen contents are not
altered, and the X server generates zero or more
Expose
events.
If backing-store was maintained while the window was unmapped, no
Expose
events
are generated.
If backing-store will now be maintained,
a full-window exposure is always generated.
Otherwise, only visible regions may be reported.
Similar tiling and exposure take place for any newly viewable inferiors.

If the window is an
InputOutput
window,
XMapWindow
generates
Expose
events on each
InputOutput
window that it causes to be displayed.
If the client maps and paints the window
and if the client begins processing events,
the window is painted twice.
To avoid this,
first ask for
Expose
events and then map the window,
so the client processes input events as usual.
The event list will include
Expose
for each
window that has appeared on the screen.
The client's normal response to
an
Expose
event should be to repaint the window.
This method usually leads to simpler programs and to proper interaction
with window managers.

The
XMapRaised
function
essentially is similar to
XMapWindow
in that it maps the window and all of its
subwindows that have had map requests.
However, it also raises the specified window to the top of the stack.
For additional information,
see
XMapWindow.

The
XMapSubwindows
function maps all subwindows for a specified window in top-to-bottom stacking
order.
The X server generates
Expose
events on each newly displayed window.
This may be much more efficient than mapping many windows
one at a time because the server needs to perform much of the work
only once, for all of the windows, rather than for each window.

The
XUnmapWindow
function unmaps the specified window and causes the X server to generate an
UnmapNotify
event.
If the specified window is already unmapped,
XUnmapWindow
has no effect.
Normal exposure processing on formerly obscured windows is performed.
Any child window will no longer be visible until another map call is
made on the parent.
In other words, the subwindows are still mapped but are not visible
until the parent is mapped.
Unmapping a window will generate
Expose
events on windows that were formerly obscured by it.

The
XUnmapSubwindows
function unmaps all subwindows for the specified window in bottom-to-top
stacking order.
It causes the X server to generate an
UnmapNotify
event on each subwindow and
Expose
events on formerly obscured windows.
Using this function is much more efficient than unmapping multiple windows
one at a time because the server needs to perform much of the work
only once, for all of the windows, rather than for each window.

Configuring Windows

Xlib provides functions that you can use to
move a window, resize a window, move and resize a window, or
change a window's border width.
To change one of these parameters,
set the appropriate member of the
XWindowChanges
structure and OR in the corresponding value mask in subsequent calls to
XConfigureWindow.
The symbols for the value mask bits and the
XWindowChanges
structure are:

The x and y members are used to set the window's x and y coordinates,
which are relative to the parent's origin
and indicate the position of the upper-left outer corner of the window.
The width and height members are used to set the inside size of the window,
not including the border, and must be nonzero, or a
BadValue
error results.
Attempts to configure a root window have no effect.

The border_width member is used to set the width of the border in pixels.
Note that setting just the border width leaves the outer-left corner of the window
in a fixed position but moves the absolute position of the window's origin.
If you attempt to set the border-width attribute of an
InputOnly
window nonzero, a
BadMatch
error results.

The sibling member is used to set the sibling window for stacking operations.
The stack_mode member is used to set how the window is to be restacked
and can be set to
Above,
Below,
TopIf,
BottomIf,
or
Opposite.

If the override-redirect flag of the window is
False
and if some other client has selected
SubstructureRedirectMask
on the parent, the X server generates a
ConfigureRequest
event, and no further processing is performed.
Otherwise,
if some other client has selected
ResizeRedirectMask
on the window and the inside
width or height of the window is being changed,
a
ResizeRequest
event is generated, and the current inside width and height are
used instead.
Note that the override-redirect flag of the window has no effect
on
ResizeRedirectMask
and that
SubstructureRedirectMask
on the parent has precedence over
ResizeRedirectMask
on the window.

When the geometry of the window is changed as specified,
the window is restacked among siblings, and a
ConfigureNotify
event is generated if the state of the window actually changes.
GravityNotify
events are generated after
ConfigureNotify
events.
If the inside width or height of the window has actually changed,
children of the window are affected as specified.

If a window's size actually changes,
the window's subwindows move according to their window gravity.
Depending on the window's bit gravity,
the contents of the window also may be moved
(see section 3.2.3).

If regions of the window were obscured but now are not,
exposure processing is performed on these formerly obscured windows,
including the window itself and its inferiors.
As a result of increasing the width or height,
exposure processing is also performed on any new regions of the window
and any regions where window contents are lost.

The restack check (specifically, the computation for
BottomIf,
TopIf,
and
Opposite)
is performed with respect to the window's final size and position (as
controlled by the other arguments of the request), not its initial position.
If a sibling is specified without a stack_mode,
a
BadMatch
error results.

If a sibling and a stack_mode are specified,
the window is restacked as follows:

Above

The window is placed just above the sibling.

Below

The window is placed just below the sibling.

TopIf

If the sibling occludes the window, the window is placed at the top of the stack.

BottomIf

If the window occludes the sibling, the window is placed at the bottom of the stack.

Opposite

If the sibling occludes the window, the window is placed at the top of the stack.
If the window occludes the sibling,
the window is placed at the bottom of the stack.

If a stack_mode is specified but no sibling is specified,
the window is restacked as follows:

Above

The window is placed at the top of the stack.

Below

The window is placed at the bottom of the stack.

TopIf

If any sibling occludes the window, the window is placed at
the top of the stack.

BottomIf

If the window occludes any sibling, the window is placed at
the bottom of the stack.

Opposite

If any sibling occludes the window, the window
is placed at the top of the stack.
If the window occludes any sibling,
the window is placed at the bottom of the stack.

Attempts to configure a root window have no effect.

To configure a window's size, location, stacking, or border, use
XConfigureWindow.

Specifies which values are to be set using information in
the values structure.
This mask is the bitwise inclusive OR of the valid configure window values bits.

values

Specifies the
XWindowChanges
structure.

The
XConfigureWindow
function uses the values specified in the
XWindowChanges
structure to reconfigure a window's size, position, border, and stacking order.
Values not specified are taken from the existing geometry of the window.

If a sibling is specified without a stack_mode or if the window
is not actually a sibling,
a
BadMatch
error results.
Note that the computations for
BottomIf,
TopIf,
and
Opposite
are performed with respect to the window's final geometry (as controlled by the
other arguments passed to
XConfigureWindow),
not its initial geometry.
Any backing store contents of the window, its
inferiors, and other newly visible windows are either discarded or
changed to reflect the current screen contents
(depending on the implementation).

Specifies the window (Wi.
of the window's border or the window itself if it has no border

x

y

Specify the x and y coordinates(Xy.

The
XMoveWindow
function moves the specified window to the specified x and y coordinates,
but it does not change the window's size, raise the window, or
change the mapping state of the window.
Moving a mapped window may or may not lose the window's contents
depending on if the window is obscured by nonchildren
and if no backing store exists.
If the contents of the window are lost,
the X server generates
Expose
events.
Moving a mapped window generates
Expose
events on any formerly obscured windows.

If the override-redirect flag of the window is
False
and some
other client has selected
SubstructureRedirectMask
on the parent, the X server generates a
ConfigureRequest
event, and no further processing is
performed.
Otherwise, the window is moved.

To change a window's size without changing the upper-left coordinate, use
XResizeWindow.

XResizeWindow(Display *display, Window w, unsignedintwidth, height);

display

Specifies the connection to the X server.

w

Specifies the window.
after the call completes

width

height

Specify the width and height(Wh.

The
XResizeWindow
function changes the inside dimensions of the specified window, not including
its borders.
This function does not change the window's upper-left coordinate or
the origin and does not restack the window.
Changing the size of a mapped window may lose its contents and generate
Expose
events.
If a mapped window is made smaller,
changing its size generates
Expose
events on windows that the mapped window formerly obscured.

If the override-redirect flag of the window is
False
and some
other client has selected
SubstructureRedirectMask
on the parent, the X server generates a
ConfigureRequest
event, and no further processing is performed.
If either width or height is zero,
a
BadValue
error results.

The
XMoveResizeWindow
function changes the size and location of the specified window
without raising it.
Moving and resizing a mapped window may generate an
Expose
event on the window.
Depending on the new size and location parameters,
moving and resizing a window may generate
Expose
events on windows that the window formerly obscured.

If the override-redirect flag of the window is
False
and some
other client has selected
SubstructureRedirectMask
on the parent, the X server generates a
ConfigureRequest
event, and no further processing is performed.
Otherwise, the window size and location are changed.

Changing Window Stacking Order

Xlib provides functions that you can use to raise, lower, circulate,
or restack windows.

To raise a window so that no sibling window obscures it, use
XRaiseWindow.

XRaiseWindow(Display *display, Window w);

display

Specifies the connection to the X server.

w

Specifies the window.

The
XRaiseWindow
function
raises the specified window to the top of the stack so that no sibling window
obscures it.
If the windows are regarded as overlapping sheets of paper stacked
on a desk,
then raising a window is analogous to moving the sheet to the top of
the stack but leaving its x and y location on the desk constant.
Raising a mapped window may generate
Expose
events for the window and any mapped subwindows that were formerly obscured.

If the override-redirect attribute of the window is
False
and some
other client has selected
SubstructureRedirectMask
on the parent, the X server generates a
ConfigureRequest
event, and no processing is performed.
Otherwise, the window is raised.

To lower a window so that it does not obscure any sibling windows, use
XLowerWindow.

XLowerWindow(Display *display, Window w);

display

Specifies the connection to the X server.

w

Specifies the window.

The
XLowerWindow
function lowers the specified window to the bottom of the stack
so that it does not obscure any sibling
windows.
If the windows are regarded as overlapping sheets of paper
stacked on a desk, then lowering a window is analogous to moving the
sheet to the bottom of the stack but leaving its x and y location on
the desk constant.
Lowering a mapped window will generate
Expose
events on any windows it formerly obscured.

If the override-redirect attribute of the window is
False
and some
other client has selected
SubstructureRedirectMask
on the parent, the X server generates a
ConfigureRequest
event, and no processing is performed.
Otherwise, the window is lowered to the bottom of the
stack.

Specifies the direction (up or down) that you want to circulate
the window.
You can pass
RaiseLowest
or
LowerHighest.

The
XCirculateSubwindows
function circulates children of the specified window in the specified
direction.
If you specify
RaiseLowest,
XCirculateSubwindows
raises the lowest mapped child (if any) that is occluded
by another child to the top of the stack.
If you specify
LowerHighest,
XCirculateSubwindows
lowers the highest mapped child (if any) that occludes another child
to the bottom of the stack.
Exposure processing is then performed on formerly obscured windows.
If some other client has selected
SubstructureRedirectMask
on the window, the X server generates a
CirculateRequest
event, and no further processing is performed.
If a child is actually restacked,
the X server generates a
CirculateNotify
event.

To raise the lowest mapped child of a window that is partially or completely
occluded by another child, use
XCirculateSubwindowsUp.

XCirculateSubwindowsUp(Display *display, Window w);

display

Specifies the connection to the X server.

w

Specifies the window.

The
XCirculateSubwindowsUp
function raises the lowest mapped child of the specified window that
is partially
or completely
occluded by another child.
Completely unobscured children are not affected.
This is a convenience function equivalent to
XCirculateSubwindows
with
RaiseLowest
specified.

To lower the highest mapped child of a window that partially or
completely occludes another child, use
XCirculateSubwindowsDown.

XCirculateSubwindowsDown(Display *display, Window w);

display

Specifies the connection to the X server.

w

Specifies the window.

The
XCirculateSubwindowsDown
function lowers the highest mapped child of the specified window that partially
or completely occludes another child.
Completely unobscured children are not affected.
This is a convenience function equivalent to
XCirculateSubwindows
with
LowerHighest
specified.

The
XRestackWindows
function restacks the windows in the order specified,
from top to bottom.
The stacking order of the first window in the windows array is unaffected,
but the other windows in the array are stacked underneath the first window,
in the order of the array.
The stacking order of the other windows is not affected.
For each window in the window array that is not a child of the specified window,
a
BadMatch
error results.

If the override-redirect attribute of a window is
False
and some
other client has selected
SubstructureRedirectMask
on the parent, the X server generates
ConfigureRequest
events for each window whose override-redirect flag is not set,
and no further processing is performed.
Otherwise, the windows will be restacked in top-to-bottom order.

Changing Window Attributes

Xlib provides functions that you can use to set window attributes.
XChangeWindowAttributes
is the more general function that allows you to set one or more window
attributes provided by the
XSetWindowAttributes
structure.
The other functions described in this section allow you to set one specific
window attribute, such as a window's background.

Specifies which window attributes are defined in the attributes
argument.
This mask is the bitwise inclusive OR of the valid attribute mask bits.
If valuemask is zero,
the attributes are ignored and are not referenced.
The values and restrictions are
the same as for
XCreateWindow.

attributes

Specifies the structure from which the values (as specified by the value mask)
are to be taken.
The value mask should have the appropriate bits
set to indicate which attributes have been set in the structure
(see section 3.2).

Depending on the valuemask,
the
XChangeWindowAttributes
function uses the window attributes in the
XSetWindowAttributes
structure to change the specified window attributes.
Changing the background does not cause the window contents to be
changed.
To repaint the window and its background, use
XClearWindow.
Setting the border or changing the background such that the
border tile origin changes causes the border to be repainted.
Changing the background of a root window to
None
or
ParentRelative
restores the default background pixmap.
Changing the border of a root window to
CopyFromParent
restores the default border pixmap.
Changing the win-gravity does not affect the current position of the
window.
Changing the backing-store of an obscured window to
WhenMapped
or
Always,
or changing the backing-planes, backing-pixel, or
save-under of a mapped window may have no immediate effect.
Changing the colormap of a window (that is, defining a new map, not
changing the contents of the existing map) generates a
ColormapNotify
event.
Changing the colormap of a visible window may have no
immediate effect on the screen because the map may not be installed
(see
XInstallColormap).
Changing the cursor of a root window to
None
restores the default
cursor.
Whenever possible, you are encouraged to share colormaps.

Multiple clients can select input on the same window.
Their event masks are maintained separately.
When an event is generated,
it is reported to all interested clients.
However, only one client at a time can select for
SubstructureRedirectMask,
ResizeRedirectMask,
and
ButtonPressMask.
If a client attempts to select any of these event masks
and some other client has already selected one,
a
BadAccess
error results.
There is only one do-not-propagate-mask for a window,
not one per client.

The
XSetWindowBackground
function sets the background of the window to the specified pixel value.
Changing the background does not cause the window contents to be changed.
XSetWindowBackground
uses a pixmap of undefined size filled with the pixel value you passed.
If you try to change the background of an
InputOnly
window, a
BadMatch
error results.

The
XSetWindowBackgroundPixmap
function sets the background pixmap of the window to the specified pixmap.
The background pixmap can immediately be freed if no further explicit
references to it are to be made.
If
ParentRelative
is specified,
the background pixmap of the window's parent is used,
or on the root window, the default background is restored.
If you try to change the background of an
InputOnly
window, a
BadMatch
error results.
If the background is set to
None,
the window has no defined background.

The
XSetWindowBorderPixmap
function sets the border pixmap of the window to the pixmap you specify.
The border pixmap can be freed immediately if no further explicit
references to it are to be made.
If you specify
CopyFromParent,
a copy of the parent window's border pixmap is used.
If you attempt to perform this on an
InputOnly
window, a
BadMatch
error results.

The
XUndefineCursor
function undoes the effect of a previous
XDefineCursor
for this window.
When the pointer is in the window,
the parent's cursor will now be used.
On the root window,
the default cursor is restored.

Chapter 4. Window Information Functions

After you connect the display to the X server and create a window, you can use the Xlib window
information functions to:

Obtain information about a window

Translate screen coordinates

Manipulate property lists

Obtain and change window properties

Manipulate selections

Obtaining Window Information

Xlib provides functions that you can use to obtain information about
the window tree, the window's current attributes,
the window's current geometry, or the current pointer coordinates.
Because they are most frequently used by window managers,
these functions all return a status to indicate whether the window still
exists.

To obtain the parent, a list of children, and number of children for
a given window, use
XQueryTree.

The
XQueryTree
function returns the root ID, the parent window ID,
a pointer to the list of children windows
(NULL when there are no children),
and the number of children in the list for the specified window.
The children are listed in current stacking order, from bottom-most
(first) to top-most (last).
XQueryTree
returns zero if it fails and nonzero if it succeeds.
To free a non-NULL children list when it is no longer needed, use
.

The x and y members are set to the upper-left outer
corner relative to the parent window's origin.
The width and height members are set to the inside size of the window,
not including the border.
The border_width member is set to the window's border width in pixels.
The depth member is set to the depth of the window
(that is, bits per pixel for the object).
The visual member is a pointer to the screen's associated
Visual
structure.
The root member is set to the root window of the screen containing the window.
The class member is set to the window's class and can be either
InputOutput
or
InputOnly.

The bit_gravity member is set to the window's bit gravity
and can be one of the following:

ForgetGravity

EastGravity

NorthWestGravity

SouthWestGravity

NorthGravity

SouthGravity

NorthEastGravity

SouthEastGravity

WestGravity

StaticGravity

The win_gravity member is set to the window's window gravity
and can be one of the following:

The backing_store member is set to indicate how the X server should maintain
the contents of a window
and can be
WhenMapped,
Always,
or
NotUseful.
The backing_planes member is set to indicate (with bits set to 1) which bit
planes of the window hold dynamic data that must be preserved in backing_stores
and during save_unders.
The backing_pixel member is set to indicate what values to use
for planes not set in backing_planes.

The save_under member is set to
True
or
False.
The colormap member is set to the colormap for the specified window and can be
a colormap ID or
None.
The map_installed member is set to indicate whether the colormap is
currently installed and can be
True
or
False.
The map_state member is set to indicate the state of the window and can be
IsUnmapped,
IsUnviewable,
or
IsViewable.
IsUnviewable
is used if the window is mapped but some ancestor is unmapped.

The all_event_masks member is set to the bitwise inclusive OR of all event
masks selected on the window by all clients.
The your_event_mask member is set to the bitwise inclusive OR of all event
masks selected by the querying client.
The do_not_propagate_mask member is set to the bitwise inclusive OR of the
set of events that should not propagate.

The override_redirect member is set to indicate whether this window overrides
structure control facilities and can be
True
or
False.
Window manager clients should ignore the window if this member is
True.

The screen member is set to a screen pointer that gives you a back pointer
to the correct screen.
This makes it easier to obtain the screen information without
having to loop over the root window fields to see which field matches.

Return the x and y coordinates that define the location of the drawable.
For a window,
these coordinates specify the upper-left outer corner relative to
its parent's origin.
For pixmaps, these coordinates are always zero.

width_return

height_return

Return the drawable's dimensions (width and height).
For a window,
these dimensions specify the inside size, not including the border.

border_width_return

Returns the border width in pixels.
If the drawable is a pixmap, it returns zero.

depth_return

Returns the depth of the drawable (bits per pixel for the object).

The
XGetGeometry
function returns the root window and the current geometry of the drawable.
The geometry of the drawable includes the x and y coordinates, width and height,
border width, and depth.
These are described in the argument list.
It is legal to pass to this function a window whose class is
InputOnly.

Translating Screen Coordinates

Applications sometimes
need to perform a coordinate transformation from the coordinate
space of one window to another window or need to determine which
window the pointing device is in.
XTranslateCoordinates
and
XQueryPointer
fulfill these needs (and avoid any race conditions) by
asking the X server to perform these operations.

To translate a coordinate in one window to the coordinate
space of another window, use
XTranslateCoordinates.

Returns the child if the coordinates are contained in a mapped child of the
destination window.

If
XTranslateCoordinates
returns
True,
it takes the src_x and src_y coordinates relative
to the source window's origin and returns these coordinates to
dest_x_return and dest_y_return
relative to the destination window's origin.
If
XTranslateCoordinates
returns
False,
src_w and dest_w are on different screens,
and dest_x_return and dest_y_return are zero.
If the coordinates are contained in a mapped child of dest_w,
that child is returned to child_return.
Otherwise, child_return is set to
None.

The
XQueryPointer
function returns the root window the pointer is logically on and the pointer
coordinates relative to the root window's origin.
If
XQueryPointer
returns
False,
the pointer is not on the same screen as the specified window, and
XQueryPointer
returns
None
to child_return and zero to win_x_return and win_y_return.
If
XQueryPointer
returns
True,
the pointer coordinates returned to win_x_return and win_y_return
are relative to the origin of the specified window.
In this case,
XQueryPointer
returns the child that contains the pointer, if any,
or else
None
to child_return.

XQueryPointer
returns the current logical state of the keyboard buttons
and the modifier keys in mask_return.
It sets mask_return to the bitwise inclusive OR of one or more
of the button or modifier key bitmasks to match
the current state of the mouse buttons and the modifier keys.

Note that the logical state of a device (as seen through Xlib)
may lag the physical state if device event processing is frozen
(see section 12.1).

Properties and Atoms

A property is a collection of named, typed data.
The window system has a set of predefined properties
(for example, the name of a window, size hints, and so on), and users can
define any other arbitrary information and associate it with windows.
Each property has a name,
which is an ISO Latin-1 string.
For each named property,
a unique identifier (atom) is associated with it.
A property also has a type, for example, string or integer.
These types are also indicated using atoms, so arbitrary new
types can be defined.
Data of only one type may be associated with a single
property name.
Clients can store and retrieve properties associated with windows.
For efficiency reasons,
an atom is used rather than a character string.
XInternAtom
can be used to obtain the atom for property names.

A property is also stored in one of several possible formats.
The X server can store the information as 8-bit quantities, 16-bit
quantities, or 32-bit quantities.
This permits the X server to present the data in the byte order that the
client expects.
If you define further properties of complex type,
you must encode and decode them yourself.
These functions must be carefully written if they are to be portable.
For further information about how to write a library extension,
see appendix C.
The type of a property is defined by an atom, which allows for
arbitrary extension in this type scheme.

Certain property names are
predefined in the server for commonly used functions.
The atoms for these properties are defined in
<X11/Xatom.h>.
To avoid name clashes with user symbols, the
#define
name for each atom has the XA_ prefix.
For an explanation of the functions that let you get and set
much of the information stored in these predefined properties,
see chapter 14.

Specifies a Boolean value that indicates whether the atom must be created.

The
XInternAtom
function returns the atom identifier associated with the specified atom_name
string.
If only_if_exists is
False,
the atom is created if it does not exist.
Therefore,
XInternAtom
can return
None.
If the atom name is not in the Host Portable Character Encoding,
the result is implementation-dependent.
Uppercase and lowercase matter;
the strings “thing”, “Thing”, and “thinG”
all designate different atoms.
The atom will remain defined even after the client's connection closes.
It will become undefined only when the last connection to
the X server closes.

Specifies a Boolean value that indicates whether the atom must be created.

atoms_return

Returns the atoms.

The
XInternAtoms
function returns the atom identifiers associated with the specified names.
The atoms are stored in the atoms_return array supplied by the caller.
Calling this function is equivalent to calling
XInternAtom
for each of the names in turn with the specified value of only_if_exists,
but this function minimizes the number of round-trip protocol exchanges
between the client and the X server.

This function returns a nonzero status if atoms are returned for
all of the names;
otherwise, it returns zero.

The
XGetAtomName
function returns the name associated with the specified atom.
If the data returned by the server is in the Latin Portable Character Encoding,
then the returned string is in the Host Portable Character Encoding.
Otherwise, the result is implementation-dependent.
To free the resulting string,
call
.

The
XGetAtomNames
function returns the names associated with the specified atoms.
The names are stored in the names_return array supplied by the caller.
Calling this function is equivalent to calling
XGetAtomName
for each of the atoms in turn,
but this function minimizes the number of round-trip protocol exchanges
between the client and the X server.

This function returns a nonzero status if names are returned for
all of the atoms;
otherwise, it returns zero.

Obtaining and Changing Window Properties

You can attach a property list to every window.
Each property has a name, a type, and a value
(see section 4.3).
The value is an array of 8-bit, 16-bit, or 32-bit quantities,
whose interpretation is left to the clients. The type
char
is used to represent 8-bit quantities, the type
short
is used to represent 16-bit quantities, and the type
long
is used to represent 32-bit quantities.

Xlib provides functions that you can use to obtain,
change, update, or interchange window properties.
In addition, Xlib provides other utility functions for inter-client
communication
(see chapter 14).

To obtain the type, format, and value of a property of a given window, use
XGetWindowProperty.

Specifies the offset in the specified property (in 32-bit quantities)
where the data is to be retrieved.

long_length

Specifies the length in 32-bit multiples of the data to be retrieved.

delete

Specifies a Boolean value that determines whether the property is deleted.

req_type

Specifies the atom identifier associated with the property type or
AnyPropertyType.

actual_type_return

Returns the atom identifier that defines the actual type of the property.

actual_format_return

Returns the actual format of the property.

nitems_return

Returns the actual number of 8-bit, 16-bit, or 32-bit items
stored in the prop_return data.

bytes_after_return

Returns the number of bytes remaining to be read in the property if
a partial read was performed.

prop_return

Returns the data in the specified format.

The
XGetWindowProperty
function returns the actual type of the property; the actual format of the property;
the number of 8-bit, 16-bit, or 32-bit items transferred; the number of bytes remaining
to be read in the property; and a pointer to the data actually returned.
XGetWindowProperty
sets the return arguments as follows:

If the specified property does not exist for the specified window,
XGetWindowProperty
returns
None
to actual_type_return and the value zero to
actual_format_return and bytes_after_return.
The nitems_return argument is empty.
In this case, the delete argument is ignored.

If the specified property exists
but its type does not match the specified type,
XGetWindowProperty
returns the actual property type to actual_type_return,
the actual property format (never zero) to actual_format_return,
and the property length in bytes
(even if the actual_format_return is 16 or 32)
to bytes_after_return.
It also ignores the delete argument.
The nitems_return argument is empty.

If the specified property exists and either you assign
AnyPropertyType
to the req_type argument or the specified type matches the actual property type,
XGetWindowProperty
returns the actual property type to actual_type_return and the actual
property format (never zero) to actual_format_return.
It also returns a value to bytes_after_return and nitems_return, by
defining the following
values:

The returned value starts at byte index I in the property (indexing
from zero), and its length in bytes is L.
If the value for long_offset causes L to be negative,
a
BadValue
error results.
The value of bytes_after_return is A,
giving the number of trailing unread bytes in the stored property.

If the returned format is 8, the returned data is represented as a
char
array.
If the returned format is 16, the returned data is represented as a
short
array and should be cast to that type to obtain the elements.
If the returned format is 32, the returned data is represented as a
long
array and should be cast to that type to obtain the elements.

XGetWindowProperty
always allocates one extra byte in prop_return
(even if the property is zero length)
and sets it to zero so that simple properties consisting of characters
do not have to be copied into yet another string before use.

If delete is
True
and bytes_after_return is zero,
XGetWindowProperty
deletes the property
from the window and generates a
PropertyNotify
event on the window.

The function returns
Success
if it executes successfully.
To free the resulting data,
use
.

The
XListProperties
function returns a pointer to an array of atom properties that are defined for
the specified window or returns NULL if no properties were found.
To free the memory allocated by this function, use
.

Specifies the type of the property.
The X server does not interpret the type but simply
passes it back to an application that later calls
XGetWindowProperty.

format

Specifies whether the data should be viewed as a list
of 8-bit, 16-bit, or 32-bit quantities.
Possible values are 8, 16, and 32.
This information allows the X server to correctly perform
byte-swap operations as necessary.
If the format is 16-bit or 32-bit,
you must explicitly cast your data pointer to an (unsigned char *) in the call
to
XChangeProperty.

mode

Specifies the mode of the operation.
You can pass
PropModeReplace,
PropModePrepend,
or
PropModeAppend.

data

Specifies the property data.

nelements

Specifies the number of elements of the specified data format.

The
XChangeProperty
function alters the property for the specified window and
causes the X server to generate a
PropertyNotify
event on that window.
XChangeProperty
performs the following:

If mode is
PropModeReplace,
XChangeProperty
discards the previous property value and stores the new data.

If mode is
PropModePrepend
or
PropModeAppend,
XChangeProperty
inserts the specified data before the beginning of the existing data
or onto the end of the existing data, respectively.
The type and format must match the existing property value,
or a
BadMatch
error results.
If the property is undefined,
it is treated as defined with the correct type and
format with zero-length data.

If the specified format is 8, the property data must be a
char
array.
If the specified format is 16, the property data must be a
short
array.
If the specified format is 32, the property data must be a
long
array.

The lifetime of a property is not tied to the storing client.
Properties remain until explicitly deleted, until the window is destroyed,
or until the server resets.
For a discussion of what happens when the connection to the X server is closed,
see section 2.6.
The maximum size of a property is server dependent and can vary dynamically
depending on the amount of memory the server has available.
(If there is insufficient space, a
BadAlloc
error results.)

The
XRotateWindowProperties
function allows you to rotate properties on a window and causes
the X server to generate
PropertyNotify
events.
If the property names in the properties array are viewed as being numbered
starting from zero and if there are num_prop property names in the list,
then the value associated with property name I becomes the value associated
with property name (I + npositions) mod N for all I from zero to N − 1.
The effect is to rotate the states by npositions places around the virtual ring
of property names (right for positive npositions,
left for negative npositions).
If npositions mod N is nonzero,
the X server generates a
PropertyNotify
event for each property in the order that they are listed in the array.
If an atom occurs more than once in the list or no property with that
name is defined for the window,
a
BadMatch
error results.
If a
BadAtom
or
BadMatch
error results,
no properties are changed.

The
XDeleteProperty
function deletes the specified property only if the
property was defined on the specified window
and causes the X server to generate a
PropertyNotify
event on the window unless the property does not exist.

Selections

Selections are one method used by applications to exchange data.
By using the property mechanism,
applications can exchange data of arbitrary types and can negotiate
the type of the data.
A selection can be thought of as an indirect property with a dynamic type.
That is, rather than having the property stored in the X server,
the property is maintained by some client (the owner).
A selection is global in nature (considered to belong to the user
but be maintained by clients) rather than being private to a particular
window subhierarchy or a particular set of clients.

Xlib provides functions that you can use to set, get, or request conversion
of selections.
This allows applications to implement the notion of current selection,
which requires that notification be sent to applications when they no
longer own the selection.
Applications that support selection often highlight the current selection
and so must be informed when another application has
acquired the selection so that they can unhighlight the selection.

When a client asks for the contents of
a selection, it specifies a selection target type.
This target type
can be used to control the transmitted representation of the contents.
For example, if the selection is “the last thing the user clicked on”
and that is currently an image, then the target type might specify
whether the contents of the image should be sent in XY format or Z format.

The target type can also be used to control the class of
contents transmitted, for example,
asking for the “looks” (fonts, line
spacing, indentation, and so forth) of a paragraph selection, not the
text of the paragraph.
The target type can also be used for other
purposes.
The protocol does not constrain the semantics.

Specifies the owner of the specified selection atom.
You can pass a window or
None.

time

Specifies the time.
You can pass either a timestamp or
CurrentTime.

The
XSetSelectionOwner
function changes the owner and last-change time for the specified selection
and has no effect if the specified time is earlier than the current
last-change time of the specified selection
or is later than the current X server time.
Otherwise, the last-change time is set to the specified time,
with
CurrentTime
replaced by the current server time.
If the owner window is specified as
None,
then the owner of the selection becomes
None
(that is, no owner).
Otherwise, the owner of the selection becomes the client executing
the request.

If the new owner (whether a client or
None)
is not
the same as the current owner of the selection and the current
owner is not
None,
the current owner is sent a
SelectionClear
event.
If the client that is the owner of a selection is later
terminated (that is, its connection is closed)
or if the owner window it has specified in the request is later
destroyed,
the owner of the selection automatically
reverts to
None,
but the last-change time is not affected.
The selection atom is uninterpreted by the X server.
XGetSelectionOwner
returns the owner window, which is reported in
SelectionRequest
and
SelectionClear
events.
Selections are global to the X server.

The
XGetSelectionOwner
function
returns the window ID associated with the window that currently owns the
specified selection.
If no selection was specified, the function returns the constant
None.
If
None
is returned,
there is no owner for the selection.

Chapter 5. Pixmap and Cursor Functions

Creating and Freeing Pixmaps

Pixmaps can only be used on the screen on which they were created.
Pixmaps are off-screen resources that are used for various operations,
such as defining cursors as tiling patterns
or as the source for certain raster operations.
Most graphics requests can operate either on a window or on a pixmap.
A bitmap is a single bit-plane pixmap.

The
XCreatePixmap
function creates a pixmap of the width, height, and depth you specified
and returns a pixmap ID that identifies it.
It is valid to pass an
InputOnly
window to the drawable argument.
The width and height arguments must be nonzero,
or a
BadValue
error results.
The depth argument must be one of the depths supported by the screen
of the specified drawable,
or a
BadValue
error results.

The server uses the specified drawable to determine on which screen
to create the pixmap.
The pixmap can be used only on this screen
and only with other drawables of the same depth (see
XCopyPlane
for an exception to this rule).
The initial contents of the pixmap are undefined.

To free all storage associated with a specified pixmap, use
XFreePixmap.

XFreePixmap(Display *display, Pixmap pixmap);

display

Specifies the connection to the X server.

pixmap

Specifies the pixmap.

The
XFreePixmap
function first deletes the association between the pixmap ID and the pixmap.
Then, the X server frees the pixmap storage when there are no references to it.
The pixmap should never be referenced again.

Creating, Recoloring, and Freeing Cursors

Each window can have a different cursor defined for it.
Whenever the pointer is in a visible window,
it is set to the cursor defined for that window.
If no cursor was defined for that window,
the cursor is the one defined for the parent window.

From X's perspective,
a cursor consists of a cursor source, mask, colors, and a hotspot.
The mask pixmap determines the shape of the cursor and must be a depth
of one.
The source pixmap must have a depth of one,
and the colors determine the colors of the source.
The hotspot defines the point on the cursor that is reported
when a pointer event occurs.
There may be limitations imposed by the hardware on
cursors as to size and whether a mask is implemented.
XQueryBestCursor
can be used to find out what sizes are possible.
There is a standard font for creating cursors, but
Xlib provides functions that you can use to create cursors
from an arbitrary font or from bitmaps.

X provides a set of standard cursor shapes in a special font named
cursor.
Applications are encouraged to use this interface for their cursors
because the font can be customized for the individual display type.
The shape argument specifies which glyph of the standard fonts
to use.

The hotspot comes from the information stored in the cursor font.
The initial colors of a cursor are a black foreground and a white
background (see
XRecolorCursor).
For further information about cursor shapes,
see appendix B.

The
XCreateGlyphCursor
function is similar to
XCreatePixmapCursor
except that the source and mask bitmaps are obtained from the specified
font glyphs.
The source_char must be a defined glyph in source_font,
or a
BadValue
error results.
If mask_font is given,
mask_char must be a defined glyph in mask_font,
or a
BadValue
error results.
The mask_font and character are optional.
The origins of the source_char and mask_char (if defined) glyphs are
positioned coincidently and define the hotspot.
The source_char and mask_char need not have the same bounding box metrics,
and there is no restriction on the placement of the hotspot relative to the bounding
boxes.
If no mask_char is given, all pixels of the source are displayed.
You can free the fonts immediately by calling
XFreeFont
if no further explicit references to them are to be made.

For 2-byte matrix fonts,
the 16-bit value should be formed with the byte1
member in the most significant byte and the byte2 member in the
least significant byte.

The
XCreatePixmapCursor
function creates a cursor and returns the cursor ID associated with it.
The foreground and background RGB values must be specified using
foreground_color and background_color,
even if the X server only has a
StaticGray
or
GrayScale
screen.
The foreground color is used for the pixels set to 1 in the
source, and the background color is used for the pixels set to 0.
Both source and mask, if specified, must have depth one (or a
BadMatch
error results) but can have any root.
The mask argument defines the shape of the cursor.
The pixels set to 1 in the mask define which source pixels are displayed,
and the pixels set to 0 define which pixels are ignored.
If no mask is given,
all pixels of the source are displayed.
The mask, if present, must be the same size as the pixmap defined by the
source argument, or a
BadMatch
error results.
The hotspot must be a point within the source,
or a
BadMatch
error results.

The components of the cursor can be transformed arbitrarily to meet
display limitations.
The pixmaps can be freed immediately if no further explicit references
to them are to be made.
Subsequent drawing in the source or mask pixmap has an undefined effect on the
cursor.
The X server might or might not make a copy of the pixmap.

Return the best width and height that is closest to the specified width
and height.

Some displays allow larger cursors than other displays.
The
XQueryBestCursor
function provides a way to find out what size cursors are actually
possible on the display.
It returns the largest size that can be displayed.
Applications should be prepared to use smaller cursors on displays that
cannot support large ones.

The
XRecolorCursor
function changes the color of the specified cursor, and
if the cursor is being displayed on a screen,
the change is visible immediately.
The pixel members of the
XColor
structures are ignored; only the RGB values are used.

The
XFreeCursor
function deletes the association between the cursor resource ID
and the specified cursor.
The cursor storage is freed when no other resource references it.
The specified cursor ID should not be referred to again.

Each X window always has an associated colormap that
provides a level of indirection between pixel values and colors displayed
on the screen.
Xlib provides functions that you can use to manipulate a colormap.
The X protocol defines colors using values in the RGB color space.
The RGB color space is device dependent;
rendering an RGB value on differing output devices typically results
in different colors.
Xlib also provides a means for clients to specify color using
device-independent color spaces for consistent results across devices.
Xlib supports device-independent color spaces derivable from the CIE XYZ
color space.
This includes the CIE XYZ, xyY, L*u*v*, and L*a*b* color spaces as well as
the TekHVC color space.

This chapter discusses how to:

Create, copy, and destroy a colormap

Specify colors by name or value

Allocate, modify, and free color cells

Read entries in a colormap

Convert between color spaces

Control aspects of color conversion

Query the color gamut of a screen

Add new color spaces

All functions, types, and symbols in this chapter with the prefix “Xcms”
are defined in
<X11/Xcms.h>.
The remaining functions and types are defined in
<X11/Xlib.h>.

Functions in this chapter manipulate the representation of color on the
screen.
For each possible value that a pixel can take in a window,
there is a color cell in the colormap.
For example,
if a window is 4 bits deep, pixel values 0 through 15 are defined.
A colormap is a collection of color cells.
A color cell consists of a triple of red, green, and blue (RGB) values.
The hardware imposes limits on the number of significant
bits in these values.
As each pixel is read out of display memory, the pixel
is looked up in a colormap.
The RGB value of the cell determines what color is displayed on the screen.
On a grayscale display with a black-and-white monitor,
the values are combined to determine the brightness on the screen.

Typically, an application allocates color cells or sets of color cells
to obtain the desired colors.
The client can allocate read-only cells.
In which case,
the pixel values for these colors can be shared among multiple applications,
and the RGB value of the cell cannot be changed.
If the client allocates read/write cells,
they are exclusively owned by the client,
and the color associated with the pixel value can be changed at will.
Cells must be allocated (and, if read/write, initialized with an RGB value)
by a client to obtain desired colors.
The use of pixel value for an
unallocated cell results in an undefined color.

Because colormaps are associated with windows, X supports displays
with multiple colormaps and, indeed, different types of colormaps.
If there are insufficient colormap resources in the display,
some windows will display in their true colors, and others
will display with incorrect colors.
A window manager usually controls which windows are displayed
in their true colors if more than one colormap is required for
the color resources the applications are using.
At any time, there is a set of installed colormaps for a screen.
Windows using one of the installed colormaps display with true colors, and
windows using other colormaps generally display with incorrect colors.
You can control the set of installed colormaps by using
XInstallColormap
and
XUninstallColormap.

Colormaps are local to a particular screen.
Screens always have a default colormap,
and programs typically allocate cells out of this colormap.
Generally, you should not write applications that monopolize
color resources.
Although some hardware supports multiple colormaps installed at one time,
many of the hardware displays
built today support only a single installed colormap, so the primitives
are written to encourage sharing of colormap entries between applications.

The red, green, and blue values are always in the range 0 to 65535
inclusive, independent of the number of bits actually used in the
display hardware.
The server scales these values down to the range used by the hardware.
Black is represented by (0,0,0),
and white is represented by (65535,65535,65535).
In some functions,
the flags member controls which of the red, green, and blue members is used
and can be the inclusive OR of zero or more of
DoRed,
DoGreen,
and
DoBlue.

Functions that operate on all color space values use an
XcmsColor
structure.
This structure contains a union of substructures,
each supporting color specification encoding for a particular color space.
Like the
XColor
structure, the
XcmsColor
structure contains pixel
and color specification information (the spec member in the
XcmsColor
structure).

Because the color specification can be encoded for the various color spaces,
encoding for the spec member is identified by the format member,
which is of type
XcmsColorFormat.
The following macros define standard formats.

Formats for device-independent color spaces are
distinguishable from those for device-dependent spaces by the 32nd bit.
If this bit is set,
it indicates that the color specification is in a device-dependent form;
otherwise, it is in a device-independent form.
If the 31st bit is set,
this indicates that the color space has been added to Xlib at run time
(see section 6.12.4).
The format value for a color space added at run time may be different each
time the program is executed.
If references to such a color space must be made outside the client
(for example, storing a color specification in a file),
then reference should be made by color space string prefix
(see
XcmsFormatOfPrefix
and
XcmsPrefixOfFormat).

Data types that describe the color specification encoding for the various
color spaces are defined as follows:

Red, green, and blue values appropriate for the specified output device.
XcmsRGB
values are of type unsigned short,
scaled from 0 to 65535 inclusive,
and are interchangeable with the red, green, and blue values in an
XColor
structure.

It is important to note that RGB Intensity values are not gamma corrected
values.
In contrast,
RGB Device values generated as a result of converting color specifications
are always gamma corrected, and
RGB Device values acquired as a result of querying a colormap
or passed in by the client are assumed by Xlib to be gamma corrected.
The term RGB value in this manual always refers to an RGB Device value.

Color Strings

Xlib provides a mechanism for using string names for colors.
A color string may either contain an abstract color name
or a numerical color specification.
Color strings are case-insensitive.

Xlib supports the use of abstract color names, for example, red or blue.
A value for this abstract name is obtained by searching one or more color
name databases.
Xlib first searches zero or more client-side databases;
the number, location, and content of these databases is
implementation-dependent and might depend on the current locale.
If the name is not found, Xlib then looks for the color in the
X server's database.
If the color name is not in the Host Portable Character Encoding,
the result is implementation-dependent.

A numerical color specification
consists of a color space name and a set of values in the following syntax:

Note that h indicates the value scaled in 4 bits,
hh the value scaled in 8 bits,
hhh the value scaled in 12 bits,
and hhhh the value scaled in 16 bits, respectively.

Typical examples are the strings “rgb:ea/75/52” and “rgb:ccc/320/320”,
but mixed numbers of hexadecimal digit strings
(“rgb:ff/a5/0” and “rgb:ccc/32/0”)
are also allowed.

For backward compatibility, an older syntax for RGB Device is
supported, but its continued use is not encouraged.
The syntax is an initial sharp sign character followed by
a numeric specification, in one of the following formats:

The R, G, and B represent single hexadecimal digits.
When fewer than 16 bits each are specified,
they represent the most significant bits of the value
(unlike the “rgb:” syntax, in which values are scaled).
For example, the string “#3a7” is the same as “#3000a0007000”.

RGB Intensity String Specification

An RGB intensity specification is identified
by the prefix “rgbi:” and conforms to the following syntax:

rgbi:<red>/<green>/<blue>

Note that red, green, and blue are floating-point values
between 0.0 and 1.0, inclusive.
The input format for these values is an optional sign,
a string of numbers possibly containing a decimal point,
and an optional exponent field containing an E or e
followed by a possibly signed integer string.

Device-Independent String Specifications

The standard device-independent string specifications have
the following syntax:

All of the values (C, H, V, X, Y, Z, a, b, u, v, y, x) are
floating-point values.
The syntax for these values is an optional plus or minus sign,
a string of digits possibly containing a decimal point,
and an optional exponent field consisting of an “E” or “e”
followed by an optional plus or minus followed by a string of digits.

Color Conversion Contexts and Gamut Mapping

When Xlib converts device-independent color specifications
into device-dependent specifications and vice versa,
it uses knowledge about the color limitations of the screen hardware.
This information, typically called the device profile,
is available in a Color Conversion Context (CCC).

Because a specified color may be outside the color gamut of the target screen
and the white point associated with the color specification may differ
from the white point inherent to the screen,
Xlib applies gamut mapping when it encounters certain conditions:

Gamut compression occurs when conversion of device-independent
color specifications to device-dependent color specifications
results in a color out of the target screen's gamut.

White adjustment occurs when the inherent white point of the screen
differs from the white point assumed by the client.

Gamut handling methods are stored as callbacks in the CCC,
which in turn are used by the color space conversion routines.
Client data is also stored in the CCC for each callback.
The CCC also contains the white point the client assumes to be
associated with color specifications (that is, the Client White Point).
The client can specify the gamut handling callbacks and client data
as well as the Client White Point.
Xlib does not preclude the X client from performing other
forms of gamut handling (for example, gamut expansion);
however, Xlib does not provide direct support for gamut handling
other than white adjustment and gamut compression.

Associated with each colormap is an initial CCC transparently generated by
Xlib.
Therefore,
when you specify a colormap as an argument to an Xlib function,
you are indirectly specifying a CCC.
There is a default CCC associated with each screen.
Newly created CCCs inherit attributes from the default CCC,
so the default CCC attributes can be modified to affect new CCCs.

Xcms functions in which gamut mapping can occur return
Status
and have specific status values defined for them,
as follows:

XcmsFailure
indicates that the function failed.

XcmsSuccess
indicates that the function succeeded.
In addition,
if the function performed any color conversion,
the colors did not need to be compressed.

XcmsSuccessWithCompression
indicates the function performed color conversion
and at least one of the colors needed to be compressed.
The gamut compression method is determined by the gamut compression
procedure in the CCC that is specified directly as a function argument
or in the CCC indirectly specified by means of the colormap argument.

Specifies a visual type supported on the screen.
If the visual type is not one supported by the screen,
a
BadMatch
error results.

alloc

Specifies the colormap entries to be allocated.
You can pass
AllocNone
or
AllocAll.

The
XCreateColormap
function creates a colormap of the specified visual type for the screen
on which the specified window resides and returns the colormap ID
associated with it.
Note that the specified window is only used to determine the screen.

The initial values of the colormap entries are undefined for the
visual classes
GrayScale,
PseudoColor,
and
DirectColor.
For
StaticGray,
StaticColor,
and
TrueColor,
the entries have defined values,
but those values are specific to the visual and are not defined by X.
For
StaticGray,
StaticColor,
and
TrueColor,
alloc must be
AllocNone,
or a
BadMatch
error results.
For the other visual classes,
if alloc is
AllocNone,
the colormap initially has no allocated entries,
and clients can allocate them.
For information about the visual types,
see section 3.1.

If alloc is
AllocAll,
the entire colormap is allocated writable.
The initial values of all allocated entries are undefined.
For
GrayScale
and
PseudoColor,
the effect is as if an
XAllocColorCells
call returned all pixel values from zero to N - 1,
where N is the colormap entries value in the specified visual.
For
DirectColor,
the effect is as if an
XAllocColorPlanes
call returned a pixel value of zero and red_mask, green_mask,
and blue_mask values containing the same bits as the corresponding
masks in the specified visual.
However, in all cases,
none of these entries can be freed by using
XFreeColors.

To create a new colormap when the allocation out of a previously
shared colormap has failed because of resource exhaustion, use
XCopyColormapAndFree.

Colormap XCopyColormapAndFree(Display *display, Colormap colormap);

display

Specifies the connection to the X server.

colormap

Specifies the colormap.

The
XCopyColormapAndFree
function creates a colormap of the same visual type and for the same screen
as the specified colormap and returns the new colormap ID.
It also moves all of the client's existing allocation from the specified
colormap to the new colormap with their color values intact
and their read-only or writable characteristics intact and frees those entries
in the specified colormap.
Color values in other entries in the new colormap are undefined.
If the specified colormap was created by the client with alloc set to
AllocAll,
the new colormap is also created with
AllocAll,
all color values for all entries are copied from the specified colormap,
and then all entries in the specified colormap are freed.
If the specified colormap was not created by the client with
AllocAll,
the allocations to be moved are all those pixels and planes
that have been allocated by the client using
XAllocColor,
XAllocNamedColor,
XAllocColorCells,
or
XAllocColorPlanes
and that have not been freed since they were allocated.

The
XFreeColormap
function deletes the association between the colormap resource ID
and the colormap and frees the colormap storage.
However, this function has no effect on the default colormap for a screen.
If the specified colormap is an installed map for a screen,
it is uninstalled (see
XUninstallColormap).
If the specified colormap is defined as the colormap for a window (by
XCreateWindow,
XSetWindowColormap,
or
XChangeWindowAttributes),
XFreeColormap
changes the colormap associated with the window to
None
and generates a
ColormapNotify
event.
X does not define the colors displayed for a window with a colormap of
None.

The
XLookupColor
function looks up the string name of a color with respect to the screen
associated with the specified colormap.
It returns both the exact color values and
the closest values provided by the screen
with respect to the visual type of the specified colormap.
If the color name is not in the Host Portable Character Encoding,
the result is implementation-dependent.
Use of uppercase or lowercase does not matter.
XLookupColor
returns nonzero if the name is resolved;
otherwise, it returns zero.

Returns the exact color value for later use and sets the
DoRed,
DoGreen,
and
DoBlue
flags.

The
XParseColor
function looks up the string name of a color with respect to the screen
associated with the specified colormap.
It returns the exact color value.
If the color name is not in the Host Portable Character Encoding,
the result is implementation-dependent.
Use of uppercase or lowercase does not matter.
XParseColor
returns nonzero if the name is resolved;
otherwise, it returns zero.

Returns the color specification parsed from the color string
or parsed from the corresponding string found in a color-name database.

color_screen_return

Returns the color that can be reproduced on the screen.

result_format

Specifies the color format for the returned color
specifications (color_screen_return and color_exact_return arguments).
If the format is
XcmsUndefinedFormat
and the color string contains a
numerical color specification,
the specification is returned in the format used in that numerical
color specification.
If the format is
XcmsUndefinedFormat
and the color string contains a color name,
the specification is returned in the format used
to store the color in the database.

The
XcmsLookupColor
function looks up the string name of a color with respect to the screen
associated with the specified colormap.
It returns both the exact color values and
the closest values provided by the screen
with respect to the visual type of the specified colormap.
The values are returned in the format specified by result_format.
If the color name is not in the Host Portable Character Encoding,
the result is implementation-dependent.
Use of uppercase or lowercase does not matter.
XcmsLookupColor
returns
XcmsSuccess
or
XcmsSuccessWithCompression
if the name is resolved; otherwise, it returns
XcmsFailure.
If
XcmsSuccessWithCompression
is returned, the color specification returned in
color_screen_return is the result of gamut compression.

Allocating and Freeing Color Cells

There are two ways of allocating color cells:
explicitly as read-only entries, one pixel value at a time,
or read/write,
where you can allocate a number of color cells and planes simultaneously.
A read-only cell has its RGB value set by the server.
Read/write cells do not have defined colors initially;
functions described in the next section must be used to store values into them.
Although it is possible for any client to store values into a read/write
cell allocated by another client,
read/write cells normally should be considered private to the client
that allocated them.

Read-only colormap cells are shared among clients.
The server counts each allocation and freeing of the cell by clients.
When the last client frees a shared cell, the cell is finally deallocated.
If a single client allocates the same read-only cell multiple
times, the server counts each such allocation, not just the first one.

To allocate a read-only color cell with an RGB value, use
XAllocColor.

The
XAllocColor
function allocates a read-only colormap entry corresponding to the closest
RGB value supported by the hardware.
XAllocColor
returns the pixel value of the color closest to the specified
RGB elements supported by the hardware
and returns the RGB value actually used.
The corresponding colormap cell is read-only.
In addition,
XAllocColor
returns nonzero if it succeeded or zero if it failed.
Multiple clients that request the same effective RGB value can be assigned
the same read-only entry, thus allowing entries to be shared.
When the last client deallocates a shared cell, it is deallocated.
XAllocColor
does not use or affect the flags in the
XColor
structure.

Specifies the color to allocate and returns the pixel and color
that is actually used in the colormap.

result_format

Specifies the color format for the returned color specification.

The
XcmsAllocColor
function is similar to
XAllocColor
except the color can be specified in any format.
The
XcmsAllocColor
function ultimately calls
XAllocColor
to allocate a read-only color cell (colormap entry) with the specified color.
XcmsAllocColor
first converts the color specified
to an RGB value and then passes this to
XAllocColor.
XcmsAllocColor
returns the pixel value of the color cell and the color specification
actually allocated.
This returned color specification is the result of converting the RGB value
returned by
XAllocColor
into the format specified with the result_format argument.
If there is no interest in a returned color specification,
unnecessary computation can be bypassed if result_format is set to
XcmsRGBFormat.
The corresponding colormap cell is read-only.
If this routine returns
XcmsFailure,
the color_in_out color specification is left unchanged.

The
XAllocNamedColor
function looks up the named color with respect to the screen that is
associated with the specified colormap.
It returns both the exact database definition and
the closest color supported by the screen.
The allocated color cell is read-only.
The pixel value is returned in screen_def_return.
If the color name is not in the Host Portable Character Encoding,
the result is implementation-dependent.
Use of uppercase or lowercase does not matter.
If screen_def_return and exact_def_return
point to the same structure, the pixel field will be set correctly,
but the color values are undefined.
XAllocNamedColor
returns nonzero if a cell is allocated;
otherwise, it returns zero.

Returns the pixel value of the color cell and color specification
that actually is stored for that cell.

color_exact_return

Returns the color specification parsed from the color string
or parsed from the corresponding string found in a color-name database.

result_format

Specifies the color format for the returned color
specifications (color_screen_return and color_exact_return arguments).
If the format is
XcmsUndefinedFormat
and the color string contains a
numerical color specification,
the specification is returned in the format used in that numerical
color specification.
If the format is
XcmsUndefinedFormat
and the color string contains a color name,
the specification is returned in the format used
to store the color in the database.

The
XcmsAllocNamedColor
function is similar to
XAllocNamedColor
except that the color returned can be in any format specified.
This function
ultimately calls
XAllocColor
to allocate a read-only color cell with
the color specified by a color string.
The color string is parsed into an
XcmsColor
structure (see
XcmsLookupColor),
converted
to an RGB value, and finally passed to
XAllocColor.
If the color name is not in the Host Portable Character Encoding,
the result is implementation-dependent.
Use of uppercase or lowercase does not matter.

This function returns both the color specification as a result
of parsing (exact specification) and the actual color specification
stored (screen specification).
This screen specification is the result of converting the RGB value
returned by
XAllocColor
into the format specified in result_format.
If there is no interest in a returned color specification,
unnecessary computation can be bypassed if result_format is set to
XcmsRGBFormat.
If color_screen_return and color_exact_return
point to the same structure, the pixel field will be set correctly,
but the color values are undefined.

Specifies a Boolean value that indicates whether the planes must be contiguous.

plane_mask_return

Returns an array of plane masks.

nplanes

Specifies the number of plane masks that are to be returned in the plane masks
array.

pixels_return

Returns an array of pixel values.

npixels

Specifies the number of pixel values that are to be returned in the
pixels_return array.

The
XAllocColorCells
function allocates read/write color cells.
The number of colors must be positive and the number of planes nonnegative,
or a
BadValue
error results.
If ncolors and nplanes are requested,
then ncolors pixels
and nplane plane masks are returned.
No mask will have any bits set to 1 in common with
any other mask or with any of the pixels.
By ORing together each pixel with zero or more masks,
ncolors × 2nplanes
distinct pixels can be produced.
All of these are
allocated writable by the request.
For
GrayScale
or
PseudoColor,
each mask has exactly one bit set to 1.
For
DirectColor,
each has exactly three bits set to 1.
If contig is
True
and if all masks are ORed
together, a single contiguous set of bits set to 1 will be formed for
GrayScale
or
PseudoColor
and three contiguous sets of bits set to 1 (one within each
pixel subfield) for
DirectColor.
The RGB values of the allocated
entries are undefined.
XAllocColorCells
returns nonzero if it succeeded or zero if it failed.

Specifies a Boolean value that indicates whether the planes must be contiguous.

pixels_return

Returns an array of pixel values.
XAllocColorPlanes
returns the pixel values in this array.

ncolors

Specifies the number of pixel values that are to be returned in the
pixels_return array.

nreds

ngreens

nblues

Specify the number of red, green, and blue planes.
The value you pass must be nonnegative.

rmask_return

gmask_return

bmask_return

Return bit masks for the red, green, and blue planes.

The specified ncolors must be positive;
and nreds, ngreens, and nblues must be nonnegative,
or a
BadValue
error results.
If ncolors colors, nreds reds, ngreens greens, and nblues blues are requested,
ncolors pixels are returned; and the masks have nreds, ngreens, and
nblues bits set to 1, respectively.
If contig is
True,
each mask will have
a contiguous set of bits set to 1.
No mask will have any bits set to 1 in common with
any other mask or with any of the pixels.
For
DirectColor,
each mask
will lie within the corresponding pixel subfield.
By ORing together
subsets of masks with each pixel value,
ncolors × 2(nreds+ngreens+nblues)
distinct pixel values can be produced.
All of these are allocated by the request.
However, in the
colormap, there are only
ncolors × 2nreds
independent red entries,
ncolors × 2ngreens
independent green entries, and
ncolors × 2nblues
independent blue entries.
This is true even for
PseudoColor.
When the colormap entry of a pixel
value is changed (using
XStoreColors,
XStoreColor,
or
XStoreNamedColor),
the pixel is decomposed according to the masks,
and the corresponding independent entries are updated.
XAllocColorPlanes
returns nonzero if it succeeded or zero if it failed.

The
XFreeColors
function frees the cells represented by pixels whose values are in the
pixels array.
The planes argument should not have any bits set to 1 in common with any of the
pixels.
The set of all pixels is produced by ORing together subsets of
the planes argument with the pixels.
The request frees all of these pixels that
were allocated by the client (using
XAllocColor,
XAllocNamedColor,
XAllocColorCells,
and
XAllocColorPlanes).
Note that freeing an
individual pixel obtained from
XAllocColorPlanes
may not actually allow
it to be reused until all of its related pixels are also freed.
Similarly,
a read-only entry is not actually freed until it has been freed by all clients,
and if a client allocates the same read-only entry multiple times,
it must free the entry that many times before the entry is actually freed.

All specified pixels that are allocated by the client in the colormap are
freed, even if one or more pixels produce an error.
If a specified pixel is not a valid index into the colormap, a
BadValue
error results.
If a specified pixel is not allocated by the
client (that is, is unallocated or is only allocated by another client)
or if the colormap was created with all entries writable (by passing
AllocAll
to
XCreateColormap),
a
BadAccess
error results.
If more than one pixel is in error,
the one that gets reported is arbitrary.

The
XStoreColor
function changes the colormap entry of the pixel value specified in the
pixel member of the
XColor
structure.
You specified this value in the
pixel member of the
XColor
structure.
This pixel value must be a read/write cell and a valid index into the colormap.
If a specified pixel is not a valid index into the colormap,
a
BadValue
error results.
XStoreColor
also changes the red, green, and/or blue color components.
You specify which color components are to be changed by setting
DoRed,
DoGreen,
and/or
DoBlue
in the flags member of the
XColor
structure.
If the colormap is an installed map for its screen,
the changes are visible immediately.

Specifies the number of
XColor
structures in the color definition array.

The
XStoreColors
function changes the colormap entries of the pixel values
specified in the pixel members of the
XColor
structures.
You specify which color components are to be changed by setting
DoRed,
DoGreen,
and/or
DoBlue
in the flags member of the
XColor
structures.
If the colormap is an installed map for its screen, the
changes are visible immediately.
XStoreColors
changes the specified pixels if they are allocated writable in the colormap
by any client, even if one or more pixels generates an error.
If a specified pixel is not a valid index into the colormap, a
BadValue
error results.
If a specified pixel either is unallocated or is allocated read-only, a
BadAccess
error results.
If more than one pixel is in error,
the one that gets reported is arbitrary.

Specifies the color cell and the color to store.
Values specified in this
XcmsColor
structure remain unchanged on return.

The
XcmsStoreColor
function converts the color specified in the
XcmsColor
structure into RGB values.
It then uses this RGB specification in an
XColor
structure, whose three flags
(DoRed,
DoGreen,
and
DoBlue)
are set, in a call to
XStoreColor
to change the color cell specified by the pixel member of the
XcmsColor
structure.
This pixel value must be a valid index for the specified colormap,
and the color cell specified by the pixel value must be a read/write cell.
If the pixel value is not a valid index, a
BadValue
error results.
If the color cell is unallocated or is allocated read-only, a
BadAccess
error results.
If the colormap is an installed map for its screen,
the changes are visible immediately.

Note that
XStoreColor
has no return value; therefore, an
XcmsSuccess
return value from this function indicates that the conversion
to RGB succeeded and the call to
XStoreColor
was made.
To obtain the actual color stored, use
XcmsQueryColor.
Because of the screen's hardware limitations or gamut compression,
the color stored in the colormap may not be identical
to the color specified.

Specifies the color specification array of
XcmsColor
structures, each specifying a color cell and the color to store in that
cell.
Values specified in the array remain unchanged upon return.

ncolors

Specifies the number of
XcmsColor
structures in the color-specification array.

compression_flags_return

Returns an array of Boolean values indicating compression status.
If a non-NULL pointer is supplied,
each element of the array is set to
True
if the corresponding color was compressed and
False
otherwise.
Pass NULL if the compression status is not useful.

The
XcmsStoreColors
function converts the colors specified in the array of
XcmsColor
structures into RGB values and then uses these RGB specifications in
XColor
structures, whose three flags
(DoRed,
DoGreen,
and
DoBlue)
are set, in a call to
XStoreColors
to change the color cells specified by the pixel member of the corresponding
XcmsColor
structure.
Each pixel value must be a valid index for the specified colormap,
and the color cell specified by each pixel value must be a read/write cell.
If a pixel value is not a valid index, a
BadValue
error results.
If a color cell is unallocated or is allocated read-only, a
BadAccess
error results.
If more than one pixel is in error,
the one that gets reported is arbitrary.
If the colormap is an installed map for its screen,
the changes are visible immediately.

Note that
XStoreColors
has no return value; therefore, an
XcmsSuccess
return value from this function indicates that conversions
to RGB succeeded and the call to
XStoreColors
was made.
To obtain the actual colors stored, use
XcmsQueryColors.
Because of the screen's hardware limitations or gamut compression,
the colors stored in the colormap may not be identical
to the colors specified.

The
XStoreNamedColor
function looks up the named color with respect to the screen associated with
the colormap and stores the result in the specified colormap.
The pixel argument determines the entry in the colormap.
The flags argument determines which of the red, green, and blue components
are set.
You can set this member to the
bitwise inclusive OR of the bits
DoRed,
DoGreen,
and
DoBlue.
If the color name is not in the Host Portable Character Encoding,
the result is implementation-dependent.
Use of uppercase or lowercase does not matter.
If the specified pixel is not a valid index into the colormap, a
BadValue
error results.
If the specified pixel either is unallocated or is allocated read-only, a
BadAccess
error results.

The
XQueryColor
and
XQueryColors
functions take pixel values in the pixel member of
XColor
structures and store in the structures the RGB values for those
pixels from the specified colormap.
The values returned for an unallocated entry are undefined.
These functions also set the flags member in the
XColor
structure to all three colors.
If a pixel is not a valid index into the specified colormap, a
BadValue
error results.
If more than one pixel is in error,
the one that gets reported is arbitrary.

Specifies the pixel member that indicates the color cell to query.
The color specification stored for the color cell is returned in this
XcmsColor
structure.

result_format

Specifies the color format for the returned color specification.

The
XcmsQueryColor
function obtains the RGB value
for the pixel value in the pixel member of the specified
XcmsColor
structure and then
converts the value to the target format as
specified by the result_format argument.
If the pixel is not a valid index in the specified colormap, a
BadValue
error results.

Specifies an array of
XcmsColor
structures, each pixel member indicating the color cell to query.
The color specifications for the color cells are returned in these structures.

ncolors

Specifies the number of
XcmsColor
structures in the color-specification array.

result_format

Specifies the color format for the returned color specification.

The
XcmsQueryColors
function obtains the RGB values
for pixel values in the pixel members of
XcmsColor
structures and then
converts the values to the target format as
specified by the result_format argument.
If a pixel is not a valid index into the specified colormap, a
BadValue
error results.
If more than one pixel is in error,
the one that gets reported is arbitrary.

Color Conversion Context Functions

Associated with each colormap is an initial CCC transparently generated by
Xlib.
Therefore, when you specify a colormap as an argument to a function,
you are indirectly specifying a CCC.
The CCC attributes that can be modified by the X client are:

Client White Point

Gamut compression procedure and client data

White point adjustment procedure and client data

The initial values for these attributes are implementation specific.
The CCC attributes for subsequently created CCCs can be defined
by changing the CCC attributes of the default CCC.
There is a default CCC associated with each screen.

The
XcmsCCCOfColormap
function returns the CCC associated with the specified colormap.
Once obtained,
the CCC attributes can be queried or modified.
Unless the CCC associated with the specified colormap is changed with
XcmsSetCCCOfColormap,
this CCC is used when the specified colormap is used as an argument
to color functions.

The
XcmsSetCCCOfColormap
function changes the CCC associated with the specified colormap.
It returns the CCC previously associated with the colormap.
If they are not used again in the application,
CCCs should be freed by calling
XcmsFreeCCC.
Several colormaps may share the same CCC without restriction; this
includes the CCCs generated by Xlib with each colormap. Xlib, however,
creates a new CCC with each new colormap.

Obtaining the Default Color Conversion Context

You can change the default CCC attributes for subsequently created CCCs
by changing the CCC attributes of the default CCC.
A default CCC is associated with each screen.

The
XcmsDefaultCCC
function returns the default CCC for the specified screen.
Its visual is the default visual of the screen.
Its initial gamut compression and white point
adjustment procedures as well as the associated client data are implementation
specific.

Color Conversion Context Macros

Applications should not directly modify any part of the
XcmsCCC.
The following lists the C language macros, their corresponding function
equivalents for other language bindings, and what data they both
can return.

DisplayOfCCC(XcmsCCC ccc);

Display *XcmsDisplayOfCCC(XcmsCCC ccc);

ccc

Specifies the CCC.

Both return the display associated with the specified CCC.

VisualOfCCC(XcmsCCC ccc);

Visual *XcmsVisualOfCCC(XcmsCCC ccc);

ccc

Specifies the CCC.

Both return the visual associated with the specified CCC.

ScreenNumberOfCCC(XcmsCCC ccc);

int XcmsScreenNumberOfCCC(XcmsCCC ccc);

ccc

Specifies the CCC.

Both return the number of the screen associated with the specified CCC.

ScreenWhitePointOfCCC(XcmsCCC ccc);

XcmsColor XcmsScreenWhitePointOfCCC(XcmsCCC ccc);

ccc

Specifies the CCC.

Both return the white point of the screen associated with the specified CCC.

ClientWhitePointOfCCC(XcmsCCC ccc);

XcmsColor *XcmsClientWhitePointOfCCC(XcmsCCC ccc);

ccc

Specifies the CCC.

Both return the Client White Point of the specified CCC.

Modifying Attributes of a Color Conversion Context

The
XcmsSetWhitePoint
function changes the Client White Point in the specified CCC.
Note that the pixel member is ignored
and that the color specification is left unchanged upon return.
The format for the new white point must be
XcmsCIEXYZFormat,
XcmsCIEuvYFormat,
XcmsCIExyYFormat,
or
XcmsUndefinedFormat.
If the color argument is NULL, this function sets the format component of the
Client White Point specification to
XcmsUndefinedFormat,
indicating that the Client White Point is assumed to be the same as the
Screen White Point.

This function returns nonzero status
if the format for the new white point is valid;
otherwise, it returns zero.

To set the gamut compression procedure and corresponding client data
in a specified CCC, use
XcmsSetCompressionProc.

Specifies the gamut compression procedure that is to be applied
when a color lies outside the screen's color gamut.
If NULL is specified and a function using this CCC must convert
a color specification to a device-dependent format and encounters a color
that lies outside the screen's color gamut,
that function will return
XcmsFailure.

client_data

Specifies client data for gamut compression procedure or NULL.

The
XcmsSetCompressionProc
function first sets the gamut compression procedure and client data
in the specified CCC with the newly specified procedure and client data
and then returns the old procedure.

To set the white point adjustment procedure and corresponding client data
in a specified CCC, use
XcmsSetWhiteAdjustProc.

The
XcmsSetWhiteAdjustProc
function first sets the white point adjustment procedure and client data
in the specified CCC with the newly specified procedure and client data
and then returns the old procedure.

Creating and Freeing a Color Conversion Context

You can explicitly create a CCC within your application by calling
XcmsCreateCCC.
These created CCCs can then be used by those functions that explicitly
call for a CCC argument.
Old CCCs that will not be used by the application should be freed using
XcmsFreeCCC.

Specifies the Client White Point.
If NULL is specified,
the Client White Point is to be assumed to be the same as the
Screen White Point.
Note that the pixel member is ignored.

compression_proc

Specifies the gamut compression procedure that is to be applied
when a color lies outside the screen's color gamut.
If NULL is specified and a function using this CCC must convert
a color specification to a device-dependent format and encounters a color
that lies outside the screen's color gamut,
that function will return
XcmsFailure.

compression_client_data

Specifies client data for use by the gamut compression procedure or NULL.

white_adjust_proc

Specifies the white adjustment procedure that is to be applied
when the Client White Point differs from the Screen White Point.
NULL indicates that no white point adjustment is desired.

white_adjust_client_data

Specifies client data for use with the white point adjustment procedure or NULL.

The
XcmsCreateCCC
function creates a CCC for the specified display, screen, and visual.

Specifies the CCC.
If conversion is between device-independent color spaces only
(for example, TekHVC to CIELuv),
the CCC is necessary only to specify the Client White Point.

colors_in_out

Specifies an array of color specifications.
Pixel members are ignored and remain unchanged upon return.

ncolors

Specifies the number of
XcmsColor
structures in the color-specification array.

target_format

Specifies the target color specification format.

compression_flags_return

Returns an array of Boolean values indicating compression status.
If a non-NULL pointer is supplied,
each element of the array is set to
True
if the corresponding color was compressed and
False
otherwise.
Pass NULL if the compression status is not useful.

The
XcmsConvertColors
function converts the color specifications in the specified array of
XcmsColor
structures from their current format to a single target format,
using the specified CCC.
When the return value is
XcmsFailure,
the contents of the color specification array are left unchanged.

The array may contain a mixture of color specification formats
(for example, 3 CIE XYZ, 2 CIE Luv, and so on).
When the array contains both device-independent and
device-dependent color specifications and the target_format argument specifies
a device-dependent format (for example,
XcmsRGBiFormat,
XcmsRGBFormat),
all specifications are converted to CIE XYZ format and then to the target
device-dependent format.

Callback Functions

This section describes the gamut compression and white point
adjustment callbacks.

The gamut compression procedure specified in the CCC
is called when an attempt to convert a color specification from
XcmsCIEXYZ
to a device-dependent format (typically
XcmsRGBi)
results in a color that lies outside the screen's color gamut.
If the gamut compression procedure requires client data, this data is passed
via the gamut compression client data in the CCC.

During color specification conversion between device-independent
and device-dependent color spaces,
if a white point adjustment procedure is specified in the CCC,
it is triggered when the Client White Point and Screen White Point differ.
If required, the client data is obtained from the CCC.

Prototype Gamut Compression Procedure

The gamut compression callback interface must adhere to the
following:

Specifies an array of color specifications.
Pixel members should be ignored and must remain unchanged upon return.

ncolors

Specifies the number of
XcmsColor
structures in the color-specification array.

index

Specifies the index into the array of
XcmsColor
structures for the encountered color specification that lies outside the
screen's color gamut.
Valid values are 0 (for the first element) to ncolors - 1.

compression_flags_return

Returns an array of Boolean values for indicating compression status.
If a non-NULL pointer is supplied
and a color at a given index is compressed, then
True
should be stored at the corresponding index in this array;
otherwise, the array should not be modified.

When implementing a gamut compression procedure, consider the following
rules and assumptions:

The gamut compression procedure can attempt to compress one or multiple
specifications at a time.

When called, elements 0 to index - 1 in the color specification
array can be assumed to fall within the screen's color gamut.
In addition, these color specifications are already in some device-dependent
format (typically
XcmsRGBi).
If any modifications are made to these color specifications,
they must be in their initial device-dependent format upon return.

When called, the element in the color specification array specified
by the index argument contains the color specification outside the
screen's color gamut encountered by the calling routine.
In addition, this color specification can be assumed to be in
XcmsCIEXYZ.
Upon return, this color specification must be in
XcmsCIEXYZ.

When called, elements from index to ncolors - 1
in the color specification array may or may not fall within the
screen's color gamut.
In addition, these color specifications can be assumed to be in
XcmsCIEXYZ.
If any modifications are made to these color specifications,
they must be in
XcmsCIEXYZ
upon return.

The color specifications passed to the gamut compression procedure
have already been adjusted to the Screen White Point.
This means that at this point the color specification's white point
is the Screen White Point.

If the gamut compression procedure uses a device-independent color space not
initially accessible for use in the color management system, use
XcmsAddColorSpace
to ensure that it is added.

Supplied Gamut Compression Procedures

The following equations are useful in describing gamut compression
functions:
delim %%

The gamut compression callback procedures provided by Xlib are as follows:

XcmsCIELabClipL

This brings the encountered out-of-gamut color specification into the
screen's color gamut by reducing or increasing CIE metric lightness (L*)
in the CIE L*a*b* color space until the color is within the gamut.
If the Psychometric Chroma of the color specification
is beyond maximum for the Psychometric Hue Angle,
then while maintaining the same Psychometric Hue Angle,
the color will be clipped to the CIE L*a*b* coordinates of maximum
Psychometric Chroma.
See
XcmsCIELabQueryMaxC.
No client data is necessary.

XcmsCIELabClipab

This brings the encountered out-of-gamut color specification into the
screen's color gamut by reducing Psychometric Chroma,
while maintaining Psychometric Hue Angle,
until the color is within the gamut.
No client data is necessary.

XcmsCIELabClipLab

This brings the encountered out-of-gamut color specification into the
screen's color gamut by replacing it with CIE L*a*b* coordinates
that fall within the color gamut while maintaining the original
Psychometric Hue
Angle and whose vector to the original coordinates is the shortest attainable.
No client data is necessary.

XcmsCIELuvClipL

This brings the encountered out-of-gamut color specification into the
screen's color gamut by reducing or increasing CIE metric lightness (L*)
in the CIE L*u*v* color space until the color is within the gamut.
If the Psychometric Chroma of the color specification
is beyond maximum for the Psychometric Hue Angle,
then, while maintaining the same Psychometric Hue Angle,
the color will be clipped to the CIE L*u*v* coordinates of maximum
Psychometric Chroma.
See
XcmsCIELuvQueryMaxC.
No client data is necessary.

XcmsCIELuvClipuv

This brings the encountered out-of-gamut color specification into the
screen's color gamut by reducing
Psychometric Chroma, while maintaining Psychometric Hue Angle,
until the color is within the gamut.
No client data is necessary.

XcmsCIELuvClipLuv

This brings the encountered out-of-gamut color specification into the
screen's color gamut by replacing it with CIE L*u*v* coordinates
that fall within the color gamut while maintaining the original
Psychometric Hue
Angle and whose vector to the original coordinates is the shortest attainable.
No client data is necessary.

XcmsTekHVCClipV

This brings the encountered out-of-gamut color specification into the
screen's color gamut by reducing or increasing the Value dimension
in the TekHVC color space until the color is within the gamut.
If Chroma of the color specification is beyond maximum for the particular Hue,
then, while maintaining the same Hue,
the color will be clipped to the Value and Chroma coordinates
that represent maximum Chroma for that particular Hue.
No client data is necessary.

XcmsTekHVCClipC

This brings the encountered out-of-gamut color specification into the
screen's color gamut by reducing the Chroma dimension
in the TekHVC color space until the color is within the gamut.
No client data is necessary.

XcmsTekHVCClipVC

This brings the encountered out-of-gamut color specification into the
screen's color gamut by replacing it with TekHVC coordinates
that fall within the color gamut while maintaining the original Hue
and whose vector to the original coordinates is the shortest attainable.
No client data is necessary.

Prototype White Point Adjustment Procedure

The white point adjustment procedure interface must adhere to the following:

Specifies an array of color specifications.
Pixel members should be ignored and must remain unchanged upon return.

ncolors

Specifies the number of
XcmsColor
structures in the color-specification array.

compression_flags_return

Returns an array of Boolean values for indicating compression status.
If a non-NULL pointer is supplied
and a color at a given index is compressed, then
True
should be stored at the corresponding index in this array;
otherwise, the array should not be modified.

Supplied White Point Adjustment Procedures

White point adjustment procedures provided by Xlib are as follows:

XcmsCIELabWhiteShiftColors

This uses the CIE L*a*b* color space for adjusting the chromatic character
of colors to compensate for the chromatic differences between the source
and destination white points.
This procedure simply converts the color specifications to
XcmsCIELab
using the source white point and then converts to the target specification
format using the destination's white point.
No client data is necessary.

XcmsCIELuvWhiteShiftColors

This uses the CIE L*u*v* color space for adjusting the chromatic character
of colors to compensate for the chromatic differences between the source
and destination white points.
This procedure simply converts the color specifications to
XcmsCIELuv
using the source white point and then converts to the target specification
format using the destination's white point.
No client data is necessary.

XcmsTekHVCWhiteShiftColors

This uses the TekHVC color space for adjusting the chromatic character
of colors to compensate for the chromatic differences between the source
and destination white points.
This procedure simply converts the color specifications to
XcmsTekHVC
using the source white point and then converts to the target specification
format using the destination's white point.
An advantage of this procedure over those previously described
is an attempt to minimize hue shift.
No client data is necessary.

From an implementation point of view,
these white point adjustment procedures convert the color specifications
to a device-independent but white-point-dependent color space
(for example, CIE L*u*v*, CIE L*a*b*, TekHVC) using one white point
and then converting those specifications to the target color space
using another white point.
In other words,
the specification goes in the color space with one white point
but comes out with another white point,
resulting in a chromatic shift based on the chromatic displacement
between the initial white point and target white point.
The CIE color spaces that are assumed to be white-point-independent
are CIE u'v'Y, CIE XYZ, and CIE xyY.
When developing a custom white point adjustment procedure that uses a
device-independent color space not initially accessible for use in the
color management system, use
XcmsAddColorSpace
to ensure that it is added.

As an example,
if the CCC specifies a white point adjustment procedure
and if the Client White Point and Screen White Point differ, the
XcmsAllocColor
function will use the white point adjustment
procedure twice:

Once to convert to
XcmsRGB

A second time to convert from
XcmsRGB

For example, assume the specification is in
XcmsCIEuvY
and the adjustment procedure is
XcmsCIELuvWhiteShiftColors.
During conversion to
XcmsRGB,
the call to
XcmsAllocColor
results in the following series of color specification conversions:

From
XcmsCIEuvY
to
XcmsCIELuv
using the Client White Point

From
XcmsCIELuv
to
XcmsCIEuvY
using the Screen White Point

From
XcmsCIEuvY
to
XcmsCIEXYZ
(CIE u'v'Y and XYZ are white-point-independent color spaces)

From
XcmsCIEXYZ
to
XcmsRGBi

From
XcmsRGBi
to
XcmsRGB

The resulting RGB specification is passed to
XAllocColor,
and the RGB
specification returned by
XAllocColor
is converted back to
XcmsCIEuvY
by reversing the color conversion sequence.

Gamut Querying Functions

This section describes the gamut querying functions that Xlib provides.
These functions allow the client to query the boundary
of the screen's color gamut in terms of the CIE L*a*b*, CIE L*u*v*,
and TekHVC color spaces.
Functions are also provided that allow you to query
the color specification of:

White (full-intensity red, green, and blue)

Red (full-intensity red while green and blue are zero)

Green (full-intensity green while red and blue are zero)

Blue (full-intensity blue while red and green are zero)

Black (zero-intensity red, green, and blue)

The white point associated with color specifications passed to
and returned from these gamut querying
functions is assumed to be the Screen White Point.
This is a reasonable assumption,
because the client is trying to query the screen's color gamut.

The following naming convention is used for the Max and Min functions:

The <dimensions> consists of a letter or letters
that identify the dimensions of the color space
that are not fixed.
For example,
XcmsTekHVCQueryMaxC
is given a fixed Hue and Value for which maximum Chroma is found.

Red, Green, and Blue Queries

To obtain the color specification for black
(zero-intensity red, green, and blue), use
XcmsQueryBlack.

Specifies the CCC.
The CCC's Client White Point and white point adjustment procedures
are ignored.

target_format

Specifies the target color specification format.

color_return

Returns the color specification in the specified target format
for (Cs.
The white point associated with the returned
color specification is the Screen White Point.
The value returned in the pixel member is undefined.

The
XcmsQueryBlack
function returns the color specification in the specified target format
for zero-intensity red, green, and blue.

To obtain the color specification for blue
(full-intensity blue while red and green are zero), use
XcmsQueryBlue.

Specifies the CCC.
The CCC's Client White Point and white point adjustment procedures
are ignored.

target_format

Specifies the target color specification format.

color_return

Returns the color specification in the specified target format
for (Cs.
The white point associated with the returned
color specification is the Screen White Point.
The value returned in the pixel member is undefined.

The
XcmsQueryBlue
function returns the color specification in the specified target format
for full-intensity blue while red and green are zero.

To obtain the color specification for green
(full-intensity green while red and blue are zero), use
XcmsQueryGreen.

Specifies the CCC.
The CCC's Client White Point and white point adjustment procedures
are ignored.

target_format

Specifies the target color specification format.

color_return

Returns the color specification in the specified target format
for (Cs.
The white point associated with the returned
color specification is the Screen White Point.
The value returned in the pixel member is undefined.

The
XcmsQueryGreen
function returns the color specification in the specified target format
for full-intensity green while red and blue are zero.

To obtain the color specification for red
(full-intensity red while green and blue are zero), use
XcmsQueryRed.

Specifies the CCC.
The CCC's Client White Point and white point adjustment procedures
are ignored.

target_format

Specifies the target color specification format.

color_return

Returns the color specification in the specified target format
for (Cs.
The white point associated with the returned
color specification is the Screen White Point.
The value returned in the pixel member is undefined.

The
XcmsQueryRed
function returns the color specification in the specified target format
for full-intensity red while green and blue are zero.

To obtain the color specification for white
(full-intensity red, green, and blue), use
XcmsQueryWhite.

Specifies the CCC.
The CCC's Client White Point and white point adjustment procedures
are ignored.

target_format

Specifies the target color specification format.

color_return

Returns the color specification in the specified target format
for (Cs.
The white point associated with the returned
color specification is the Screen White Point.
The value returned in the pixel member is undefined.

The
XcmsQueryWhite
function returns the color specification in the specified target format
for full-intensity red, green, and blue.

CIELab Queries

The following equations are useful in describing the CIELab query functions:
delim %%

Specifies the CCC.
The CCC's Client White Point and white point adjustment procedures
are ignored.

hue_angle

Specifies the hue angle (in degrees) at which to find (Ha.

L_star

Specifies the lightness (L*) at which to find (Ls.

color_return

Returns the CIE L*a*b* coordinates of (Lc
displayable by the screen for the given (lC.
The white point associated with the returned
color specification is the Screen White Point.
The value returned in the pixel member is undefined.

The
XcmsCIELabQueryMaxC
function, given a hue angle and lightness,
finds the point of maximum chroma displayable by the screen.
It returns this point in CIE L*a*b* coordinates.

To obtain the CIE L*a*b* coordinates of maximum CIE metric lightness (L*)
for a given Psychometric Hue Angle and Psychometric Chroma, use
XcmsCIELabQueryMaxL.

Specifies the CCC.
The CCC's Client White Point and white point adjustment procedures
are ignored.

hue_angle

Specifies the hue angle (in degrees) at which to find (Ha.

chroma

Specifies the chroma at which to find (Ch.

color_return

Returns the CIE L*a*b* coordinates of (Lc
displayable by the screen for the given (lC.
The white point associated with the returned
color specification is the Screen White Point.
The value returned in the pixel member is undefined.

The
XcmsCIELabQueryMaxL
function, given a hue angle and chroma,
finds the point in CIE L*a*b* color space of maximum
lightness (L*) displayable by the screen.
It returns this point in CIE L*a*b* coordinates.
An
XcmsFailure
return value usually indicates that the given chroma
is beyond maximum for the given hue angle.

To obtain the CIE L*a*b* coordinates of maximum Psychometric Chroma
for a given Psychometric Hue Angle, use
XcmsCIELabQueryMaxLC.

Specifies the CCC.
The CCC's Client White Point and white point adjustment procedures
are ignored.

hue_angle

Specifies the hue angle (in degrees) at which to find (Ha.

color_return

Returns the CIE L*a*b* coordinates of (Lc
displayable by the screen for the given (lC.
The white point associated with the returned
color specification is the Screen White Point.
The value returned in the pixel member is undefined.

The
XcmsCIELabQueryMaxLC
function, given a hue angle,
finds the point of maximum chroma displayable by the screen.
It returns this point in CIE L*a*b* coordinates.

To obtain the CIE L*a*b* coordinates of minimum CIE metric lightness (L*)
for a given Psychometric Hue Angle and Psychometric Chroma, use
XcmsCIELabQueryMinL.

Specifies the CCC.
The CCC's Client White Point and white point adjustment procedures
are ignored.

hue_angle

Specifies the hue angle (in degrees) at which to find (Ha.

chroma

Specifies the chroma at which to find (Ch.

color_return

Returns the CIE L*a*b* coordinates of (Lc
displayable by the screen for the given (lC.
The white point associated with the returned
color specification is the Screen White Point.
The value returned in the pixel member is undefined.

The
XcmsCIELabQueryMinL
function, given a hue angle and chroma,
finds the point of minimum lightness (L*) displayable by the screen.
It returns this point in CIE L*a*b* coordinates.
An
XcmsFailure
return value usually indicates that the given chroma
is beyond maximum for the given hue angle.

CIELuv Queries

The following equations are useful in describing the CIELuv query functions:
delim %%

Specifies the CCC.
The CCC's Client White Point and white point adjustment procedures
are ignored.

hue_angle

Specifies the hue angle (in degrees) at which to find (Ha.

L_star

Specifies the lightness (L*) at which to find (Ls.

color_return

Returns the CIE L*u*v* coordinates of (Lc
displayable by the screen for the given (lC.
The white point associated with the returned
color specification is the Screen White Point.
The value returned in the pixel member is undefined.

The
XcmsCIELuvQueryMaxC
function, given a hue angle and lightness,
finds the point of maximum chroma displayable by the screen.
It returns this point in CIE L*u*v* coordinates.

To obtain the CIE L*u*v* coordinates of maximum CIE metric lightness (L*)
for a given Psychometric Hue Angle and Psychometric Chroma, use
XcmsCIELuvQueryMaxL.

Specifies the CCC.
The CCC's Client White Point and white point adjustment procedures
are ignored.

hue_angle

Specifies the hue angle (in degrees) at which to find (Ha.

L_star

Specifies the lightness (L*) at which to find (Ls.

color_return

Returns the CIE L*u*v* coordinates of (Lc
displayable by the screen for the given (lC.
The white point associated with the returned
color specification is the Screen White Point.
The value returned in the pixel member is undefined.

The
XcmsCIELuvQueryMaxL
function, given a hue angle and chroma,
finds the point in CIE L*u*v* color space of maximum
lightness (L*) displayable by the screen.
It returns this point in CIE L*u*v* coordinates.
An
XcmsFailure
return value usually indicates that the given chroma
is beyond maximum for the given hue angle.

To obtain the CIE L*u*v* coordinates of maximum Psychometric Chroma
for a given Psychometric Hue Angle, use
XcmsCIELuvQueryMaxLC.

Specifies the CCC.
The CCC's Client White Point and white point adjustment procedures
are ignored.

hue_angle

Specifies the hue angle (in degrees) at which to find (Ha.

color_return

Returns the CIE L*u*v* coordinates of (Lc
displayable by the screen for the given (lC.
The white point associated with the returned
color specification is the Screen White Point.
The value returned in the pixel member is undefined.

The
XcmsCIELuvQueryMaxLC
function, given a hue angle,
finds the point of maximum chroma displayable by the screen.
It returns this point in CIE L*u*v* coordinates.

To obtain the CIE L*u*v* coordinates of minimum CIE metric lightness (L*)
for a given Psychometric Hue Angle and Psychometric Chroma, use
XcmsCIELuvQueryMinL.

Specifies the CCC.
The CCC's Client White Point and white point adjustment procedures
are ignored.

hue_angle

Specifies the hue angle (in degrees) at which to find (Ha.

chroma

Specifies the chroma at which to find (Ch.

color_return

Returns the CIE L*u*v* coordinates of (Lc
displayable by the screen for the given (lC.
The white point associated with the returned
color specification is the Screen White Point.
The value returned in the pixel member is undefined.

The
XcmsCIELuvQueryMinL
function, given a hue angle and chroma,
finds the point of minimum lightness (L*) displayable by the screen.
It returns this point in CIE L*u*v* coordinates.
An
XcmsFailure
return value usually indicates that the given chroma
is beyond maximum for the given hue angle.

TekHVC Queries

Specifies the CCC.
The CCC's Client White Point and white point adjustment procedures
are ignored.

hue

Specifies the Hue (Hu.

value

Specifies the Value in which to find the (Va.

color_return

Returns the (Lc at which the (lC was found.
The white point associated with the returned
color specification is the Screen White Point.
The value returned in the pixel member is undefined.

The
XcmsTekHVCQueryMaxC
function, given a Hue and Value,
determines the maximum Chroma in TekHVC color space
displayable by the screen.
It returns the maximum Chroma along with the actual Hue
and Value at which the maximum Chroma was found.

Specifies the CCC.
The CCC's Client White Point and white point adjustment procedures
are ignored.

hue

Specifies the Hue (Hu.

chroma

Specifies the chroma at which to find (Ch.

color_return

Returns the (Lc at which the (lC was found.
The white point associated with the returned
color specification is the Screen White Point.
The value returned in the pixel member is undefined.

The
XcmsTekHVCQueryMaxV
function, given a Hue and Chroma,
determines the maximum Value in TekHVC color space
displayable by the screen.
It returns the maximum Value and the actual Hue and Chroma
at which the maximum Value was found.

To obtain the maximum Chroma and Value at which it is reached
for a specified Hue, use
XcmsTekHVCQueryMaxVC.

Specifies the CCC.
The CCC's Client White Point and white point adjustment procedures
are ignored.

hue

Specifies the Hue (Hu.
XcmsTekHVC for the maximum Chroma, the Value at which \
that maximum Chroma is reached, and the actual Hue

color_return

Returns the (Lc at which the (lC was found.
The white point associated with the returned
color specification is the Screen White Point.
The value returned in the pixel member is undefined.

The
XcmsTekHVCQueryMaxVC
function, given a Hue,
determines the maximum Chroma in TekHVC color space displayable by the screen
and the Value at which that maximum Chroma is reached.
It returns the maximum Chroma,
the Value at which that maximum Chroma is reached,
and the actual Hue for which the maximum Chroma was found.

To obtain a specified number of TekHVC specifications such that they
contain maximum Values for a specified Hue and the
Chroma at which the maximum Values are reached, use
XcmsTekHVCQueryMaxVSamples.

Specifies the CCC.
The CCC's Client White Point and white point adjustment procedures
are ignored.

hue

Specifies the Hue (Hu.

nsamples

Specifies the number of samples.

colors_return

Returns nsamples of color specifications in XcmsTekHVC
such that the Chroma is the maximum attainable for the Value and Hue.
The white point associated with the returned
color specification is the Screen White Point.
The value returned in the pixel member is undefined.

The
XcmsTekHVCQueryMaxVSamples
returns nsamples of maximum Value, the Chroma at which that maximum Value
is reached, and the actual Hue for which the maximum Chroma was found.
These sample points may then be used to plot the maximum Value/Chroma
boundary of the screen's color gamut for the specified Hue in TekHVC color
space.

Specifies the CCC.
The CCC's Client White Point and white point adjustment procedures
are ignored.

hue

Specifies the Hue (Hu.

value

Specifies the Value in which to find the (Va.

color_return

Returns the (Lc at which the (lC was found.
The white point associated with the returned
color specification is the Screen White Point.
The value returned in the pixel member is undefined.

The
XcmsTekHVCQueryMinV
function, given a Hue and Chroma,
determines the minimum Value in TekHVC color space displayable by the screen.
It returns the minimum Value and the actual Hue and Chroma at which
the minimum Value was found.

Color Management Extensions

The Xlib color management facilities can be extended in two ways:

Device-Independent Color Spaces

Device-independent color spaces that are derivable to CIE XYZ
space can be added using the
XcmsAddColorSpace
function.

Color Characterization Function Set

A Color Characterization Function Set consists of
device-dependent color spaces and their functions that
convert between these color spaces and the CIE XYZ
color space, bundled together for a specific class of output devices.
A function set can be added using the
XcmsAddFunctionSet
function.

Color Spaces

The CIE XYZ color space serves as the hub for all
conversions between device-independent and device-dependent color spaces.
Therefore, the knowledge to convert an
XcmsColor
structure to and from CIE XYZ format is associated with each color space.
For example, conversion from CIE L*u*v* to RGB requires the knowledge
to convert from CIE L*u*v* to CIE XYZ and from CIE XYZ to RGB.
This knowledge is stored as an array of functions that,
when applied in series, will convert the
XcmsColor
structure to or from CIE XYZ format.
This color specification conversion mechanism facilitates
the addition of color spaces.

Of course, when converting between only device-independent color spaces
or only device-dependent color spaces,
shortcuts are taken whenever possible.
For example, conversion from TekHVC to CIE L*u*v* is performed
by intermediate conversion to CIE u*v*Y and then to CIE L*u*v*,
thus bypassing conversion between CIE u*v*Y and CIE XYZ.

Adding Device-Independent Color Spaces

The
XcmsAddColorSpace
function makes a device-independent color space (actually an
XcmsColorSpace
structure) accessible by the color management system.
Because format values for unregistered color spaces are assigned at run time,
they should be treated as private to the client.
If references to an unregistered color space must be made
outside the client (for example, storing color specifications
in a file using the unregistered color space),
then reference should be made by color space prefix
(see
XcmsFormatOfPrefix
and
XcmsPrefixOfFormat).

If the
XcmsColorSpace
structure is already accessible in the color management system,
XcmsAddColorSpace
returns
XcmsSuccess.

Note that added
XcmsColorSpaces
must be retained for reference by Xlib.

Querying Color Space Format and Prefix

To obtain the format associated with the color space
associated with a specified color string prefix, use
XcmsFormatOfPrefix.

XcmsColorFormat XcmsFormatOfPrefix(char *prefix);

prefix

Specifies the string that contains the color space prefix.

The
XcmsFormatOfPrefix
function returns the format for the specified color space prefix
(for example, the string “CIEXYZ”).
The prefix is case-insensitive.
If the color space is not accessible in the color management system,
XcmsFormatOfPrefix
returns
XcmsUndefinedFormat.

To obtain the color string prefix associated with the color space
specified by a color format, use
XcmsPrefixOfFormat.

char *XcmsPrefixOfFormat(XcmsColorFormat format);

format

Specifies the color specification format.

The
XcmsPrefixOfFormat
function returns the string prefix associated with the color specification
encoding specified by the format argument.
Otherwise, if no encoding is found, it returns NULL.
The returned string must be treated as read-only.

Creating Additional Color Spaces

Color space specific information necessary
for color space conversion and color string parsing is stored in an
XcmsColorSpace
structure.
Therefore, a new structure containing this information is required
for each additional color space.
In the case of device-independent color spaces,
a handle to this new structure (that is, by means of a global variable)
is usually made accessible to the client program for use with the
XcmsAddColorSpace
function.

If a new
XcmsColorSpace
structure specifies a color space not registered with the X Consortium,
they should be treated as private to the client
because format values for unregistered color spaces are assigned at run time.
If references to an unregistered color space must be made outside the
client (for example, storing color specifications in a file using the
unregistered color space), then reference should be made by color space prefix
(see
XcmsFormatOfPrefix
and
XcmsPrefixOfFormat).

The prefix member specifies the prefix that indicates a color string
is in this color space's string format.
For example, the strings “ciexyz” or “CIEXYZ” for CIE XYZ,
and “rgb” or “RGB” for RGB.
The prefix is case insensitive.
The format member specifies the color specification format.
Formats for unregistered color spaces are assigned at run time.
The parseString member contains a pointer to the function
that can parse a color string into an
XcmsColor
structure.
This function returns an integer (int): nonzero if it succeeded
and zero otherwise.
The to_CIEXYZ and from_CIEXYZ members contain pointers,
each to a NULL terminated list of function pointers.
When the list of functions is executed in series,
it will convert the color specified in an
XcmsColor
structure from/to the current color space format to/from the CIE XYZ format.
Each function returns an integer (int): nonzero if it succeeded
and zero otherwise.
The white point to be associated with the colors is specified
explicitly, even though white points can be found in the CCC.
The inverse_flag member, if nonzero, specifies that for each function listed
in to_CIEXYZ,
its inverse function can be found in from_CIEXYZ such that:

Given: n = number of functions in each list
for each i, such that 0 <= i < n
from_CIEXYZ[n - i - 1] is the inverse of to_CIEXYZ[i].

Specifies an array of color specifications.
Pixel members should be ignored and must remain unchanged upon return.

ncolors

Specifies the number of
XcmsColor
structures in the color-specification array.

compression_flags_return

Returns an array of Boolean values for indicating compression status.
If a non-NULL pointer is supplied
and a color at a given index is compressed, then
True
should be stored at the corresponding index in this array;
otherwise, the array should not be modified.

Conversion functions are available globally for use by other color
spaces.
The conversion functions provided by Xlib are:

Function

Converts from

Converts to

XcmsCIELabToCIEXYZ

XcmsCIELabFormat

XcmsCIEXYZFormat

XcmsCIELuvToCIEuvY

XcmsCIELuvFormat

XcmsCIEuvYFormat

XcmsCIEXYZToCIELab

XcmsCIEXYZFormat

XcmsCIELabFormat

XcmsCIEXYZToCIEuvY

XcmsCIEXYZFormat

XcmsCIEuvYFormat

XcmsCIEXYZToCIExyY

XcmsCIEXYZFormat

XcmsCIExyYFormat

XcmsCIEXYZToRGBi

XcmsCIEXYZFormat

XcmsRGBiFormat

XcmsCIEuvYToCIELuv

XcmsCIEuvYFormat

XcmsCIELabFormat

XcmsCIEuvYToCIEXYZ

XcmsCIEuvYFormat

XcmsCIEXYZFormat

XcmsCIEuvYToTekHVC

XcmsCIEuvYFormat

XcmsTekHVCFormat

XcmsCIExyYToCIEXYZ

XcmsCIExyYFormat

XcmsCIEXYZFormat

XcmsRGBToRGBi

XcmsRGBFormat

XcmsRGBiFormat

XcmsRGBiToCIEXYZ

XcmsRGBiFormat

XcmsCIEXYZFormat

XcmsRGBiToRGB

XcmsRGBiFormat

XcmsRGBFormat

XcmsTekHVCToCIEuvY

XcmsTekHVCFormat

XcmsCIEuvYFormat

Function Sets

Functions to convert between device-dependent color spaces
and CIE XYZ may differ for different classes of output devices
(for example, color versus gray monitors).
Therefore, the notion of a Color Characterization Function Set
has been developed.
A function set consists of device-dependent color spaces
and the functions that convert color specifications
between these device-dependent color spaces and the CIE XYZ color space
appropriate for a particular class of output devices.
The function set also contains a function that reads
color characterization data off root window properties.
It is this characterization data that will differ between devices within
a class of output devices.
For details about how color characterization data is
stored in root window properties,
see the
section on Device Color Characterization in the
Inter-Client Communication Conventions Manual.
The LINEAR_RGB function set is provided by Xlib
and will support most color monitors.
Function sets may require data that differs
from those needed for the LINEAR_RGB function set.
In that case,
its corresponding data may be stored on different root window properties.

Adding Function Sets

The
XcmsAddFunctionSet
function adds a function set to the color management system.
If the function set uses device-dependent
XcmsColorSpace
structures not accessible in the color management system,
XcmsAddFunctionSet
adds them.
If an added
XcmsColorSpace
structure is for a device-dependent color space not registered
with the X Consortium,
they should be treated as private to the client
because format values for unregistered color spaces are assigned at run time.
If references to an unregistered color space must be made outside the
client (for example, storing color specifications in a file
using the unregistered color space),
then reference should be made by color space prefix
(see
XcmsFormatOfPrefix
and
XcmsPrefixOfFormat).

Additional function sets should be added before any calls to other
Xlib routines are made.
If not, the
XcmsPerScrnInfo
member of a previously created
XcmsCCC
does not have the opportunity to initialize
with the added function set.

Creating Additional Function Sets

The creation of additional function sets should be
required only when an output device does not conform to existing
function sets or when additional device-dependent color spaces are necessary.
A function set consists primarily of a collection of device-dependent
XcmsColorSpace
structures and a means to read and store a
screen's color characterization data.
This data is stored in an
XcmsFunctionSet
structure.
A handle to this structure (that is, by means of global variable)
is usually made accessible to the client program for use with
XcmsAddFunctionSet.

If a function set uses new device-dependent
XcmsColorSpace
structures,
they will be transparently processed into the color management system.
Function sets can share an
XcmsColorSpace
structure for a device-dependent color space.
In addition, multiple
XcmsColorSpace
structures are allowed for a device-dependent color space;
however, a function set can reference only one of them.
These
XcmsColorSpace
structures will differ in the functions to convert to and from CIE XYZ,
thus tailored for the specific function set.

The DDColorSpaces member is a pointer to a NULL terminated list
of pointers to
XcmsColorSpace
structures for the device-dependent color spaces that are supported
by the function set.
The screenInitProc member is set to the callback procedure (see the following
interface specification) that initializes the
XcmsPerScrnInfo
structure for a particular screen.

The screen initialization callback must adhere to the following software
interface specification:

Specifies the
XcmsPerScrnInfo
structure, which contains the per screen information.

The screen initialization callback in the
XcmsFunctionSet
structure fetches the color characterization data (device profile) for
the specified screen,
typically off properties on the
screen's root window.
It then initializes the specified
XcmsPerScrnInfo
structure.
If successful, the procedure fills in the
XcmsPerScrnInfo
structure as follows:

It sets the screenData member to the address
of the created device profile data structure
(contents known only by the function set).

It next sets the screenWhitePoint member.

It next sets the functionSet member to the address of the
XcmsFunctionSet
structure.

It then sets the state member to
XcmsInitSuccess
and finally returns
XcmsSuccess.

If unsuccessful, the procedure sets the state member to
XcmsInitFailure
and returns
XcmsFailure.

The screenWhitePoint member specifies the white point inherent to
the screen.
The functionSet member specifies the appropriate function set.
The screenData member specifies the device profile.
The state member is set to one of the following:

XcmsInitNone
indicates initialization has not been previously attempted.

XcmsInitFailure
indicates initialization has been previously attempted but failed.

XcmsInitSuccess
indicates initialization has been previously attempted and succeeded.

The screen free callback must adhere to the following software
interface specification:

typedef void (*XcmsScreenFreeProc)(XPointer screenData);

screenData

Specifies the data to be freed.

This function is called to free the screenData stored in an
XcmsPerScrnInfo
structure.

A number of resources are used when performing graphics operations in X. Most information
about performing graphics (for example, foreground color, background color, line style, and so
on) is stored in resources called graphics contexts (GCs). Most graphics operations (see chapter
8) take a GC as an argument. Although in theory the X protocol permits sharing of GCs between
applications, it is expected that applications will use their own GCs when performing operations.
Sharing of GCs is highly discouraged because the library may cache GC state.

Graphics operations can be performed to either windows or pixmaps, which collectively are
called drawables. Each drawable exists on a single screen. A GC is created for a specific screen
and drawable depth and can only be used with drawables of matching screen and depth.

This chapter discusses how to:

Manipulate graphics context/state

Use graphics context convenience functions

Manipulating Graphics Context/State

Most attributes of graphics operations are stored in GCs.
These include line width, line style, plane mask, foreground, background,
tile, stipple, clipping region, end style, join style, and so on.
Graphics operations (for example, drawing lines) use these values
to determine the actual drawing operation.
Extensions to X may add additional components to GCs.
The contents of a GC are private to Xlib.

Xlib implements a write-back cache for all elements of a GC that are not
resource IDs to allow Xlib to implement the transparent coalescing of changes
to GCs.
For example,
a call to
XSetForeground
of a GC followed by a call to
XSetLineAttributes
results in only a single-change GC protocol request to the server.
GCs are neither expected nor encouraged to be shared between client
applications, so this write-back caching should present no problems.
Applications cannot share GCs without external synchronization.
Therefore,
sharing GCs between applications is highly discouraged.

To set an attribute of a GC,
set the appropriate member of the
XGCValues
structure and OR in the corresponding value bitmask in your subsequent calls to
XCreateGC.
The symbols for the value mask bits and the
XGCValues
structure are:

Note that foreground and background are not set to any values likely
to be useful in a window.

The function attributes of a GC are used when you update a section of
a drawable (the destination) with bits from somewhere else (the source).
The function in a GC defines how the new destination bits are to be
computed from the source bits and the old destination bits.
GXcopy
is typically the most useful because it will work on a color display,
but special applications may use other functions,
particularly in concert with particular planes of a color display.
The 16 GC functions, defined in
<X11/X.h>,
are:

Function Name

Value

Operation

GXclear

0x0

0

GXand

0x1

src AND dst

GXandReverse

0x2

src AND NOT dst

GXcopy

0x3

src

GXandInverted

0x4

(NOT src) AND dst

GXnoop

0x5

dst

GXxor

0x6

src XOR dst

GXor

0x7

src OR dst

GXnor

0x8

(NOT src) AND (NOT dst)

GXequiv

0x9

(NOT src) XOR dst

GXinvert

0xa

NOT dst

GXorReverse

0xb

src OR (NOT dst)

GXcopyInverted

0xc

NOT src

GXorInverted

0xd

(NOT src) OR dst

GXnand

0xe

(NOT src) OR (NOT dst)

GXset

0xf

1

Many graphics operations depend on either pixel values or planes in a GC.
The planes attribute is of type long, and it specifies which planes of the
destination are to be modified, one bit per plane.
A monochrome display has only one plane and
will be the least significant bit of the word.
As planes are added to the display hardware, they will occupy more
significant bits in the plane mask.

In graphics operations, given a source and destination pixel,
the result is computed bitwise on corresponding bits of the pixels.
That is, a Boolean operation is performed in each bit plane.
The plane_mask restricts the operation to a subset of planes.
A macro constant
AllPlanes
can be used to refer to all planes of the screen simultaneously.
The result is computed by the following:

((src FUNC dst) AND plane-mask) OR (dst AND (NOT plane-mask))

Range checking is not performed on the values for foreground,
background, or plane_mask.
They are simply truncated to the appropriate
number of bits.
The line-width is measured in pixels and either can be greater than or equal to
one (wide line) or can be the special value zero (thin line).

Wide lines are drawn centered on the path described by the graphics request.
Unless otherwise specified by the join-style or cap-style,
the bounding box of a wide line with endpoints [x1, y1], [x2, y2] and
width w is a rectangle with vertices at the following real coordinates:

Here sn is the sine of the angle of the line,
and cs is the cosine of the angle of the line.
A pixel is part of the line and so is drawn
if the center of the pixel is fully inside the bounding box
(which is viewed as having infinitely thin edges).
If the center of the pixel is exactly on the bounding box,
it is part of the line if and only if the interior is immediately to its right
(x increasing direction).
Pixels with centers on a horizontal edge are a special case and are part of
the line if and only if the interior or the boundary is immediately below
(y increasing direction) and the interior or the boundary is immediately
to the right (x increasing direction).

Thin lines (zero line-width) are one-pixel-wide lines drawn using an
unspecified, device-dependent algorithm.
There are only two constraints on this algorithm.

If a line is drawn unclipped from [x1,y1] to [x2,y2] and
if another line is drawn unclipped from [x1+dx,y1+dy] to [x2+dx,y2+dy],
a point [x,y] is touched by drawing the first line
if and only if the point [x+dx,y+dy] is touched by drawing the second line.

The effective set of points comprising a line cannot be affected by clipping.
That is, a point is touched in a clipped line if and only if the point
lies inside the clipping region and the point would be touched
by the line when drawn unclipped.

A wide line drawn from [x1,y1] to [x2,y2] always draws the same pixels
as a wide line drawn from [x2,y2] to [x1,y1], not counting cap-style
and join-style.
It is recommended that this property be true for thin lines,
but this is not required.
A line-width of zero may differ from a line-width of one in which pixels are
drawn.
This permits the use of many manufacturers' line drawing hardware,
which may run many times faster than the more precisely specified
wide lines.

In general,
drawing a thin line will be faster than drawing a wide line of width one.
However, because of their different drawing algorithms,
thin lines may not mix well aesthetically with wide lines.
If it is desirable to obtain precise and uniform results across all displays,
a client should always use a line-width of one rather than a line-width of zero.

The line-style defines which sections of a line are drawn:

LineSolid

The full path of the line is drawn.

LineDoubleDash

The full path of the line is drawn,
but the even dashes are filled differently
from the odd dashes (see fill-style) with
CapButt
style used where even and odd dashes meet.

LineOnOffDash

Only the even dashes are drawn,
and cap-style applies to
all internal ends of the individual dashes,
except
CapNotLast
is treated as
CapButt.

The cap-style defines how the endpoints of a path are drawn:

CapNotLast

This is equivalent to
CapButt
except that for a line-width of zero the final endpoint is not drawn.

CapButt

The line is square at the endpoint (perpendicular to the slope of the line)
with no projection beyond.

CapRound

The line has a circular arc with the diameter equal to the line-width,
centered on the endpoint.
(This is equivalent to
CapButt
for line-width of zero).

CapProjecting

The line is square at the end, but the path continues beyond the endpoint
for a distance equal to half the line-width.
(This is equivalent to
CapButt
for line-width of zero).

The join-style defines how corners are drawn for wide lines:

JoinMiter

The outer edges of two lines extend to meet at an angle.
However, if the angle is less than 11 degrees,
then a
JoinBevel
join-style is used instead.

JoinRound

The corner is a circular arc with the diameter equal to the line-width,
centered on the joinpoint.

JoinBevel

The corner has
CapButt
endpoint styles with the triangular notch filled.

For a line with coincident endpoints (x1=x2, y1=y2),
when the cap-style is applied to both endpoints,
the semantics depends on the line-width and the cap-style:

CapNotLast

thin

The results are device dependent,
but the desired effect is that nothing is drawn.

CapButt

thin

The results are device dependent,
but the desired effect is that a single pixel is drawn.

CapRound

thin

The results are the same as for
CapButt /thin.

CapProjecting

thin

The results are the same as for
CapButt /thin.

CapButt

wide

Nothing is drawn.

CapRound

wide

The closed path is a circle, centered at the endpoint, and
with the diameter equal to the line-width.

CapProjecting

wide

The closed path is a square, aligned with the coordinate axes, centered at the
endpoint, and with the sides equal to the line-width.

For a line with coincident endpoints (x1=x2, y1=y2),
when the join-style is applied at one or both endpoints,
the effect is as if the line was removed from the overall path.
However, if the total path consists of or is reduced to a single point joined
with itself, the effect is the same as when the cap-style is applied at both
endpoints.

The tile/stipple represents an infinite two-dimensional plane,
with the tile/stipple replicated in all dimensions.
When that plane is superimposed on the drawable
for use in a graphics operation, the upper-left corner
of some instance of the tile/stipple is at the coordinates within
the drawable specified by the tile/stipple origin.
The tile/stipple and clip origins are interpreted relative to the
origin of whatever destination drawable is specified in a graphics
request.
The tile pixmap must have the same root and depth as the GC,
or a
BadMatch
error results.
The stipple pixmap must have depth one and must have the same root as the
GC, or a
BadMatch
error results.
For stipple operations where the fill-style is
FillStippled
but not
FillOpaqueStippled,
the stipple pattern is tiled in a
single plane and acts as an additional clip mask to be ANDed with the clip-mask.
Although some sizes may be faster to use than others,
any size pixmap can be used for tiling or stippling.

A tile with the same width and height as stipple,
but with background everywhere stipple has a zero
and with foreground everywhere stipple has a one

FillStippled

Foreground masked by stipple

When drawing lines with line-style
LineDoubleDash,
the odd dashes are controlled by the fill-style in the following manner:

FillSolid

Background

FillTiled

Same as for even dashes

FillOpaqueStippled

Same as for even dashes

FillStippled

Background masked by stipple

Storing a pixmap in a GC might or might not result in a copy
being made.
If the pixmap is later used as the destination for a graphics request,
the change might or might not be reflected in the GC.
If the pixmap is used simultaneously in a graphics request both as
a destination and as a tile or stipple,
the results are undefined.

For optimum performance,
you should draw as much as possible with the same GC
(without changing its components).
The costs of changing GC components relative to using different GCs
depend on the display hardware and the server implementation.
It is quite likely that some amount of GC information will be
cached in display hardware and that such hardware can only cache a small number
of GCs.

The dashes value is actually a simplified form of the
more general patterns that can be set with
XSetDashes.
Specifying a
value of N is equivalent to specifying the two-element list [N, N] in
XSetDashes.
The value must be nonzero,
or a
BadValue
error results.

The clip-mask restricts writes to the destination drawable.
If the clip-mask is set to a pixmap,
it must have depth one and have the same root as the GC,
or a
BadMatch
error results.
If clip-mask is set to
None,
the pixels are always drawn regardless of the clip origin.
The clip-mask also can be set by calling the
XSetClipRectangles
or
XSetRegion
functions.
Only pixels where the clip-mask has a bit set to 1 are drawn.
Pixels are not drawn outside the area covered by the clip-mask
or where the clip-mask has a bit set to 0.
The clip-mask affects all graphics requests.
The clip-mask does not clip sources.
The clip-mask origin is interpreted relative to the origin of whatever
destination drawable is specified in a graphics request.

You can set the subwindow-mode to
ClipByChildren
or
IncludeInferiors.
For
ClipByChildren,
both source and destination windows are
additionally clipped by all viewable
InputOutput
children.
For
IncludeInferiors,
neither source nor destination window is clipped by inferiors.
This will result in including subwindow contents in the source
and drawing through subwindow boundaries of the destination.
The use of
IncludeInferiors
on a window of one depth with mapped
inferiors of differing depth is not illegal, but the semantics are
undefined by the core protocol.

The fill-rule defines what pixels are inside (drawn) for
paths given in
XFillPolygon
requests and can be set to
EvenOddRule
or
WindingRule.
For
EvenOddRule,
a point is inside if
an infinite ray with the point as origin crosses the path an odd number
of times.
For
WindingRule,
a point is inside if an infinite ray with the
point as origin crosses an unequal number of clockwise and
counterclockwise directed path segments.
A clockwise directed path segment is one that crosses the ray from left to
right as observed from the point.
A counterclockwise segment is one that crosses the ray from right to left
as observed from the point.
The case where a directed line segment is coincident with the ray is
uninteresting because you can simply choose a different ray that is not
coincident with a segment.

For both
EvenOddRule
and
WindingRule,
a point is infinitely small,
and the path is an infinitely thin line.
A pixel is inside if the center point of the pixel is inside
and the center point is not on the boundary.
If the center point is on the boundary,
the pixel is inside if and only if the polygon interior is immediately to
its right (x increasing direction).
Pixels with centers on a horizontal edge are a special case
and are inside if and only if the polygon interior is immediately below
(y increasing direction).

The arc-mode controls filling in the
XFillArcs
function and can be set to
ArcPieSlice
or
ArcChord.
For
ArcPieSlice,
the arcs are pie-slice filled.
For
ArcChord,
the arcs are chord filled.

The graphics-exposure flag controls
GraphicsExpose
event generation
for
XCopyArea
and
XCopyPlane
requests (and any similar requests defined by extensions).

To create a new GC that is usable on a given screen with a
depth of drawable, use
XCreateGC.

Specifies which components in the GC are to be (Vm.
This argument is the bitwise inclusive OR of zero or more of the valid
GC component mask bits.

values

Specifies any values as specified by the valuemask.

The
XCreateGC
function creates a graphics context and returns a GC.
The GC can be used with any destination drawable having the same root
and depth as the specified drawable.
Use with other drawables results in a
BadMatch
error.

Specifies which components in the GC are to be (Vm.
This argument is the bitwise inclusive OR of zero or more of the valid
GC component mask bits.

dest

Specifies the destination GC.

The
XCopyGC
function copies the specified components from the source GC
to the destination GC.
The source and destination GCs must have the same root and depth,
or a
BadMatch
error results.
The valuemask specifies which component to copy, as for
XCreateGC.

Specifies which components in the GC are to be (Vm.
This argument is the bitwise inclusive OR of zero or more of the valid
GC component mask bits.

values

Specifies any values as specified by the valuemask.

The
XChangeGC
function changes the components specified by valuemask for
the specified GC.
The values argument contains the values to be set.
The values and restrictions are the same as for
XCreateGC.
Changing the clip-mask overrides any previous
XSetClipRectangles
request on the context.
Changing the dash-offset or dash-list
overrides any previous
XSetDashes
request on the context.
The order in which components are verified and altered is server dependent.
If an error is generated, a subset of the components may have been altered.

Specifies which components in the GC are to be (Vm.
This argument is the bitwise inclusive OR of zero or more of the valid
GC component mask bits.

values_return

Returns the GC values in the specified
XGCValues
structure.

The
XGetGCValues
function returns the components specified by valuemask for the specified GC.
If the valuemask contains a valid set of GC mask bits
(GCFunction,
GCPlaneMask,
GCForeground,
GCBackground,
GCLineWidth,
GCLineStyle,
GCCapStyle,
GCJoinStyle,
GCFillStyle,
GCFillRule,
GCTile,
GCStipple,
GCTileStipXOrigin,
GCTileStipYOrigin,
GCFont,
GCSubwindowMode,
GCGraphicsExposures,
GCClipXOrigin,
GCClipYOrigin,
GCDashOffset,
or
GCArcMode)
and no error occurs,
XGetGCValues
sets the requested components in values_return and returns a nonzero status.
Otherwise, it returns a zero status.
Note that the clip-mask and dash-list (represented by the
GCClipMask
and
GCDashList
bits, respectively, in the valuemask)
cannot be requested.
Also note that an invalid resource ID (with one or more of the three
most significant bits set to 1) will be returned for
GCFont,
GCTile,
and
GCStipple
if the component has never been explicitly set by the client.

Xlib usually defers sending changes to the components of a GC to the server
until a graphics function is actually called with that GC.
This permits batching of component changes into a single server request.
In some circumstances, however, it may be necessary for the client
to explicitly force sending the changes to the server.
An example might be when a protocol extension uses the GC indirectly,
in such a way that the extension interface cannot know what GC will be used.
To force sending GC component changes, use
XFlushGC.

void XFlushGC(Display *display, GC gc);

display

Specifies the connection to the X server.

gc

Specifies the GC.

Using Graphics Context Convenience Routines

This section discusses how to set the:

Foreground, background, plane mask, or function components

Line attributes and dashes components

Fill style and fill rule components

Fill tile and stipple components

Font component

Clip region component

Arc mode, subwindow mode, and graphics exposure components

Setting the Foreground, Background, Function, or Plane Mask

To set the foreground, background, plane mask, and function components
for a given GC, use
XSetState.

Specifies the phase of the pattern for the dashed line-style you want to set
for the specified GC.

dash_list

Specifies the dash-list for the dashed line-style
you want to set for the specified GC.

n

Specifies the number of elements in dash_list.

The
XSetDashes
function sets the dash-offset and dash-list attributes for dashed line styles
in the specified GC.
There must be at least one element in the specified dash_list,
or a
BadValue
error results.
The initial and alternating elements (second, fourth, and so on)
of the dash_list are the even dashes, and
the others are the odd dashes.
Each element specifies a dash length in pixels.
All of the elements must be nonzero,
or a
BadValue
error results.
Specifying an odd-length list is equivalent to specifying the same list
concatenated with itself to produce an even-length list.

The dash-offset defines the phase of the pattern,
specifying how many pixels into the dash-list the pattern
should actually begin in any single graphics request.
Dashing is continuous through path elements combined with a join-style
but is reset to the dash-offset between each sequence of joined lines.

The unit of measure for dashes is the same for the ordinary coordinate system.
Ideally, a dash length is measured along the slope of the line, but implementations
are only required to match this ideal for horizontal and vertical lines.
Failing the ideal semantics, it is suggested that the length be measured along the
major axis of the line.
The major axis is defined as the x axis for lines drawn at an angle of between
−45 and +45 degrees or between 135 and 225 degrees from the x axis.
For all other lines, the major axis is the y axis.

Setting the Fill Tile and Stipple

Some displays have hardware support for tiling or
stippling with patterns of specific sizes.
Tiling and stippling operations that restrict themselves to those specific
sizes run much faster than such operations with arbitrary size patterns.
Xlib provides functions that you can use to determine the best size,
tile, or stipple for the display
as well as to set the tile or stipple shape and the tile or stipple origin.

To obtain the best size of a tile, stipple, or cursor, use
XQueryBestSize.

Specifies the class that you are interested in.
You can pass
TileShape,
CursorShape,
or
StippleShape.

which_screen

Specifies any drawable on the screen.

width

height

Specify the width and height.

width_return

height_return

Return the width and height of the object best supported
by the display hardware.

The
XQueryBestSize
function returns the best or closest size to the specified size.
For
CursorShape,
this is the largest size that can be fully displayed on the screen specified by
which_screen.
For
TileShape,
this is the size that can be tiled fastest.
For
StippleShape,
this is the size that can be stippled fastest.
For
CursorShape,
the drawable indicates the desired screen.
For
TileShape
and
StippleShape,
the drawable indicates the screen and possibly the window class and depth.
An
InputOnly
window cannot be used as the drawable for
TileShape
or
StippleShape,
or a
BadMatch
error results.

Return the width and height of the object best supported
by the display hardware.

The
XQueryBestTile
function returns the best or closest size, that is, the size that can be
tiled fastest on the screen specified by which_screen.
The drawable indicates the screen and possibly the window class and depth.
If an
InputOnly
window is used as the drawable, a
BadMatch
error results.

Return the width and height of the object best supported
by the display hardware.

The
XQueryBestStipple
function returns the best or closest size, that is, the size that can be
stippled fastest on the screen specified by which_screen.
The drawable indicates the screen and possibly the window class and depth.
If an
InputOnly
window is used as the drawable, a
BadMatch
error results.

Specifies the ordering relations on the rectangles.
You can pass
Unsorted,
YSorted,
YXSorted,
or
YXBanded.

The
XSetClipRectangles
function changes the clip-mask in the specified GC
to the specified list of rectangles and sets the clip origin.
The output is clipped to remain contained within the
rectangles.
The clip-origin is interpreted relative to the origin of
whatever destination drawable is specified in a graphics request.
The rectangle coordinates are interpreted relative to the clip-origin.
The rectangles should be nonintersecting, or the graphics results will be
undefined.
Note that the list of rectangles can be empty,
which effectively disables output.
This is the opposite of passing
None
as the clip-mask in
XCreateGC,
XChangeGC,
and
XSetClipMask.

If known by the client, ordering relations on the rectangles can be
specified with the ordering argument.
This may provide faster operation
by the server.
If an incorrect ordering is specified, the X server may generate a
BadMatch
error, but it is not required to do so.
If no error is generated, the graphics
results are undefined.
Unsorted
means the rectangles are in arbitrary order.
YSorted
means that the rectangles are nondecreasing in their Y origin.
YXSorted
additionally constrains
YSorted
order in that all
rectangles with an equal Y origin are nondecreasing in their X
origin.
YXBanded
additionally constrains
YXSorted
by requiring that,
for every possible Y scanline, all rectangles that include that
scanline have an identical Y origins and Y extents.

Once you have established a connection to a display, you can use the Xlib graphics functions to:

Clear and copy areas

Draw points, lines, rectangles, and arcs

Fill areas

Manipulate fonts

Draw text

Transfer images between clients and the server

If the same drawable and GC is used for each call, Xlib batches back-to-back
calls to XDrawPoint, XDrawLine, XDrawRectangle, XFillArc, and XFillRectangle.
Note that this reduces the total number of requests sent to the server.

Clearing Areas

Xlib provides functions that you can use to clear an area or the entire window.
Because pixmaps do not have defined backgrounds,
they cannot be filled by using the functions described in this section.
Instead, to accomplish an analogous operation on a pixmap,
you should use
XFillRectangle,
which sets the pixmap to a known value.

Specifies the window.
and specify the upper-left corner of the rectangle

x

y

Specify the x and y coordinates(Xy.

width

height

Specify the width and height(Wh.

exposures

Specifies a Boolean value that indicates if
Expose
events are to be generated.

The
XClearArea
function paints a rectangular area in the specified window according to the
specified dimensions with the window's background pixel or pixmap.
The subwindow-mode effectively is
ClipByChildren.
If width is zero, it
is replaced with the current width of the window minus x.
If height is
zero, it is replaced with the current height of the window minus y.
If the window has a defined background tile,
the rectangle clipped by any children is filled with this tile.
If the window has
background
None,
the contents of the window are not changed.
In either
case, if exposures is
True,
one or more
Expose
events are generated for regions of the rectangle that are either visible or are
being retained in a backing store.
If you specify a window whose class is
InputOnly,
a
BadMatch
error results.

The
XClearWindow
function clears the entire area in the specified window and is
equivalent to
XClearArea
(display, w, 0, 0, 0, 0,
False).
If the window has a defined background tile, the rectangle is tiled with a
plane-mask of all ones and
GXcopy
function.
If the window has
background
None,
the contents of the window are not changed.
If you specify a window whose class is
InputOnly,
a
BadMatch
error results.

Specify the x and y coordinates,
which are relative to the origin of the source rectangle
and specify its upper-left corner.
and destination rectangles

width

height

Specify the width and height(Wh.
and specify its upper-left corner

dest_x

dest_y

Specify the x and y coordinates(Dx.

The
XCopyArea
function combines the specified rectangle of src with the specified rectangle
of dest.
The drawables must have the same root and depth,
or a
BadMatch
error results.

If regions of the source rectangle are obscured and have not been
retained in backing store
or if regions outside the boundaries of the source drawable are specified,
those regions are not copied.
Instead, the
following occurs on all corresponding destination regions that are either
visible or are retained in backing store.
If the destination is a window with a background other than
None,
corresponding regions
of the destination are tiled with that background
(with plane-mask of all ones and
GXcopy
function).
Regardless of tiling or whether the destination is a window or a pixmap,
if graphics-exposures is
True,
then
GraphicsExpose
events for all corresponding destination regions are generated.
If graphics-exposures is
True
but no
GraphicsExpose
events are generated, a
NoExpose
event is generated.
Note that by default graphics-exposures is
True
in new GCs.

Specify the x and y coordinates,
which are relative to the origin of the source rectangle
and specify its upper-left corner.

width

height

Specify the width and height(Wh.
and specify its upper-left corner

dest_x

dest_y

Specify the x and y coordinates(Dx.

plane

Specifies the bit plane.
You must set exactly one bit to 1.

The
XCopyPlane
function uses a single bit plane of the specified source rectangle
combined with the specified GC to modify the specified rectangle of dest.
The drawables must have the same root but need not have the same depth.
If the drawables do not have the same root, a
BadMatch
error results.
If plane does not have exactly one bit set to 1 and the value of plane
is not less than %2 sup n%, where n is the depth of src, a
BadValue
error results.

Effectively,
XCopyPlane
forms a pixmap of the same depth as the rectangle of dest and with a
size specified by the source region.
It uses the foreground/background pixels in the GC (foreground
everywhere the bit plane in src contains a bit set to 1,
background everywhere the bit plane in src contains a bit set to 0)
and the equivalent of a
CopyArea
protocol request is performed with all the same exposure semantics.
This can also be thought of as using the specified region of the source
bit plane as a stipple with a fill-style of
FillOpaqueStippled
for filling a rectangular area of the destination.

All x and y members are signed integers.
The width and height members are 16-bit unsigned integers.
You should be careful not to generate coordinates and sizes
out of the 16-bit ranges, because the protocol only has 16-bit fields
for these values.

Specifies the coordinate mode.
You can pass
CoordModeOrigin
or
CoordModePrevious.

The
XDrawPoint
function uses the foreground pixel and function components of the
GC to draw a single point into the specified drawable;
XDrawPoints
draws multiple points this way.
CoordModeOrigin
treats all coordinates as relative to the origin,
and
CoordModePrevious
treats all coordinates after the first as relative to the previous point.
XDrawPoints
draws the points in the order listed in the array.

The
XDrawLine
function uses the components of the specified GC to
draw a line between the specified set of points (x1, y1) and (x2, y2).
It does not perform joining at coincident endpoints.
For any given line,
XDrawLine
does not draw a pixel more than once.
If lines intersect, the intersecting pixels are drawn multiple times.

The
XDrawLines
function uses the components of the specified GC to draw
npoints-1 lines between each pair of points (point[i], point[i+1])
in the array of
XPoint
structures.
It draws the lines in the order listed in the array.
The lines join correctly at all intermediate points, and if the first and last
points coincide, the first and last lines also join correctly.
For any given line,
XDrawLines
does not draw a pixel more than once.
If thin (zero line-width) lines intersect,
the intersecting pixels are drawn multiple times.
If wide lines intersect, the intersecting pixels are drawn only once, as though
the entire
PolyLine
protocol request were a single, filled shape.
CoordModeOrigin
treats all coordinates as relative to the origin,
and
CoordModePrevious
treats all coordinates after the first as relative to the previous point.

The
XDrawSegments
function draws multiple, unconnected lines.
For each segment,
XDrawSegments
draws a
line between (x1, y1) and (x2, y2).
It draws the lines in the order listed in the array of
XSegment
structures and does not perform joining at coincident endpoints.
For any given line,
XDrawSegments
does not draw a pixel more than once.
If lines intersect, the intersecting pixels are drawn multiple times.

All three functions use these GC components:
function, plane-mask, line-width,
line-style, cap-style, fill-style, subwindow-mode,
clip-x-origin, clip-y-origin, and clip-mask.
The
XDrawLines
function also uses the join-style GC component.
All three functions also use these GC mode-dependent components:
foreground, background, tile, stipple, tile-stipple-x-origin,
tile-stipple-y-origin, dash-offset, and dash-list.

The
XDrawRectangle
and
XDrawRectangles
functions draw the outlines of the specified rectangle or rectangles as
if a five-point
PolyLine
protocol request were specified for each rectangle:

[x,y] [x+width,y] [x+width,y+height] [x,y+height] [x,y]

For the specified rectangle or rectangles,
these functions do not draw a pixel more than once.
XDrawRectangles
draws the rectangles in the order listed in the array.
If rectangles intersect,
the intersecting pixels are drawn multiple times.

delim %%
XDrawArc
draws a single circular or elliptical arc, and
XDrawArcs
draws multiple circular or elliptical arcs.
Each arc is specified by a rectangle and two angles.
The center of the circle or ellipse is the center of the
rectangle, and the major and minor axes are specified by the width and height.
Positive angles indicate counterclockwise motion,
and negative angles indicate clockwise motion.
If the magnitude of angle2 is greater than 360 degrees,
XDrawArc
or
XDrawArcs
truncates it to 360 degrees.

For an arc specified as %[ ~x, ~y, ~width , ~height, ~angle1, ~angle2 ]%,
the origin of the major and minor axes is at
% [ x +^ {width over 2} , ~y +^ {height over 2} ]%,
and the infinitely thin path describing the entire circle or ellipse
intersects the horizontal axis at % [ x, ~y +^ {height over 2} ]% and
% [ x +^ width , ~y +^ { height over 2 }] %
and intersects the vertical axis at % [ x +^ { width over 2 } , ~y ]% and
% [ x +^ { width over 2 }, ~y +^ height ]%.
These coordinates can be fractional
and so are not truncated to discrete coordinates.
The path should be defined by the ideal mathematical path.
For a wide line with line-width lw,
the bounding outlines for filling are given
by the two infinitely thin paths consisting of all points whose perpendicular
distance from the path of the circle/ellipse is equal to lw/2
(which may be a fractional value).
The cap-style and join-style are applied the same as for a line
corresponding to the tangent of the circle/ellipse at the endpoint.

For an arc specified as % [ ~x, ~y, ~width, ~height, ~angle1, ~angle2 ]%,
the angles must be specified
in the effectively skewed coordinate system of the ellipse (for a
circle, the angles and coordinate systems are identical). The
relationship between these angles and angles expressed in the normal
coordinate system of the screen (as measured with a protractor) is as
follows:

The skewed-angle and normal-angle are expressed in radians (rather
than in degrees scaled by 64) in the range % [ 0 , ~2 pi ]% and where atan
returns a value in the range % [ - pi over 2 , ~pi over 2 ] %
and adjust is:

For any given arc,
XDrawArc
and
XDrawArcs
do not draw a pixel more than once.
If two arcs join correctly and if the line-width is greater than zero
and the arcs intersect,
XDrawArc
and
XDrawArcs
do not draw a pixel more than once.
Otherwise,
the intersecting pixels of intersecting arcs are drawn multiple times.
Specifying an arc with one endpoint and a clockwise extent draws the same pixels
as specifying the other endpoint and an equivalent counterclockwise extent,
except as it affects joins.

If the last point in one arc coincides with the first point in the following
arc, the two arcs will join correctly.
If the first point in the first arc coincides with the last point in the last
arc, the two arcs will join correctly.
By specifying one axis to be zero, a horizontal or vertical line can be
drawn.
Angles are computed based solely on the coordinate system and ignore the
aspect ratio.

The
XFillRectangle
and
XFillRectangles
functions fill the specified rectangle or rectangles
as if a four-point
FillPolygon
protocol request were specified for each rectangle:

[x,y] [x+width,y] [x+width,y+height] [x,y+height]

Each function uses the x and y coordinates,
width and height dimensions, and GC you specify.

XFillRectangles
fills the rectangles in the order listed in the array.
For any given rectangle,
XFillRectangle
and
XFillRectangles
do not draw a pixel more than once.
If rectangles intersect, the intersecting pixels are
drawn multiple times.

Both functions use these GC components:
function, plane-mask, fill-style, subwindow-mode,
clip-x-origin, clip-y-origin, and clip-mask.
They also use these GC mode-dependent components:
foreground, background, tile, stipple, tile-stipple-x-origin,
and tile-stipple-y-origin.

Specifies a shape that helps the server to improve performance.
You can pass
Complex,
Convex,
or
Nonconvex.

mode

Specifies the coordinate mode.
You can pass
CoordModeOrigin
or
CoordModePrevious.

XFillPolygon
fills the region closed by the specified path.
The path is closed
automatically if the last point in the list does not coincide with the
first point.
XFillPolygon
does not draw a pixel of the region more than once.
CoordModeOrigin
treats all coordinates as relative to the origin,
and
CoordModePrevious
treats all coordinates after the first as relative to the previous point.

Depending on the specified shape, the following occurs:

If shape is
Complex,
the path may self-intersect.
Note that contiguous coincident points in the path are not treated
as self-intersection.

If shape is
Convex,
for every pair of points inside the polygon,
the line segment connecting them does not intersect the path.
If known by the client,
specifying
Convex
can improve performance.
If you specify
Convex
for a path that is not convex,
the graphics results are undefined.

If shape is
Nonconvex,
the path does not self-intersect, but the shape is not
wholly convex.
If known by the client,
specifying
Nonconvex
instead of
Complex
may improve performance.
If you specify
Nonconvex
for a self-intersecting path, the graphics results are undefined.

The fill-rule of the GC controls the filling behavior of
self-intersecting polygons.

For each arc,
XFillArc
or
XFillArcs
fills the region closed by the infinitely thin path
described by the specified arc and, depending on the
arc-mode specified in the GC, one or two line segments.
For
ArcChord,
the single line segment joining the endpoints of the arc is used.
For
ArcPieSlice,
the two line segments joining the endpoints of the arc with the center
point are used.
XFillArcs
fills the arcs in the order listed in the array.
For any given arc,
XFillArc
and
XFillArcs
do not draw a pixel more than once.
If regions intersect,
the intersecting pixels are drawn multiple times.

Both functions use these GC components:
function, plane-mask, fill-style, arc-mode, subwindow-mode, clip-x-origin,
clip-y-origin, and clip-mask.
They also use these GC mode-dependent components:
foreground, background, tile, stipple, tile-stipple-x-origin,
and tile-stipple-y-origin.

Font Metrics

A font is a graphical description of a set of characters that are used to
increase efficiency whenever a set of small, similar sized patterns are
repeatedly used.

This section discusses how to:

Load and free fonts

Obtain and free font names

Compute character string sizes

Compute logical extents

Query character string sizes

The X server loads fonts whenever a program requests a new font.
The server can cache fonts for quick lookup.
Fonts are global across all screens in a server.
Several levels are possible when dealing with fonts.
Most applications simply use
XLoadQueryFont
to load a font and query the font metrics.

Characters in fonts are regarded as masks.
Except for image text requests,
the only pixels modified are those in which bits are set to 1 in the character.
This means that it makes sense to draw text using stipples or tiles
(for example, many menus gray-out unusable entries).

The
XFontStruct
structure contains all of the information for the font
and consists of the font-specific information as well as
a pointer to an array of
XCharStruct
structures for the
characters contained in the font.
The
XFontStruct,
XFontProp,
and
XCharStruct
structures contain:

typedef struct {
short lbearing; /* origin to left edge of raster */
short rbearing; /* origin to right edge of raster */
short width; /* advance to next char's origin */
short ascent; /* baseline to top edge of raster */
short descent; /* baseline to bottom edge of raster */
unsigned short attributes; /* per char flags (not predefined) */
} XCharStruct;

X supports single byte/character, two bytes/character matrix,
and 16-bit character text operations.
Note that any of these forms can be used with a font, but a
single byte/character text request can only specify a single byte
(that is, the first row of a 2-byte font).
You should view 2-byte fonts as a two-dimensional matrix of defined
characters: byte1 specifies the range of defined rows and
byte2 defines the range of defined columns of the font.
Single byte/character fonts have one row defined, and the byte2 range
specified in the structure defines a range of characters.

The bounding box of a character is defined by the
XCharStruct
of that character.
When characters are absent from a font,
the default_char is used.
When fonts have all characters of the same size,
only the information in the
XFontStruct
min and max bounds are used.

The members of the
XFontStruct
have the following semantics:

The direction member can be either
FontLeftToRight
or
FontRightToLeft.
It is just a hint as to whether most
XCharStruct
elements
have a positive
(FontLeftToRight)
or a negative
(FontRightToLeft)
character width
metric.
The core protocol defines no support for vertical text.

If the min_byte1 and max_byte1 members are both zero, min_char_or_byte2
specifies the linear character index corresponding to the first element
of the per_char array, and max_char_or_byte2 specifies the linear character
index of the last element.

If either min_byte1 or max_byte1 are nonzero, both
min_char_or_byte2 and max_char_or_byte2 are less than 256,
and the 2-byte character index values corresponding to the
per_char array element N (counting from 0) are:

If the per_char pointer is NULL,
all glyphs between the first and last character indexes
inclusive have the same information,
as given by both min_bounds and max_bounds.

If all_chars_exist is
True,
all characters in the per_char array have nonzero bounding boxes.

The default_char member specifies the character that will be used when an
undefined or nonexistent character is printed.
The default_char is a 16-bit character (not a 2-byte character).
For a font using 2-byte matrix format,
the default_char has byte1 in the most-significant byte
and byte2 in the least significant byte.
If the default_char itself specifies an undefined or nonexistent character,
no printing is performed for an undefined or nonexistent character.

The min_bounds and max_bounds members contain the most extreme values of
each individual
XCharStruct
component over all elements of this array
(and ignore nonexistent characters).
The bounding box of the font (the smallest
rectangle enclosing the shape obtained by superimposing all of the
characters at the same origin [x,y]) has its upper-left coordinate at:

[x + min_bounds.lbearing, y - max_bounds.ascent]

Its width is:

max_bounds.rbearing - min_bounds.lbearing

Its height is:

max_bounds.ascent + max_bounds.descent

The ascent member is the logical extent of the font above the baseline that is
used for determining line spacing.
Specific characters may extend beyond
this.

The descent member is the logical extent of the font at or below the
baseline that is used for determining line spacing.
Specific characters may extend beyond this.

If the baseline is at Y-coordinate y,
the logical extent of the font is inclusive between the Y-coordinate
values (y - font.ascent) and (y + font.descent - 1).
Typically,
the minimum interline spacing between rows of text is given
by ascent + descent.

For a character origin at [x,y],
the bounding box of a character (that is,
the smallest rectangle that encloses the character's shape)
described in terms of
XCharStruct
components is a rectangle with its upper-left corner at:

[x + lbearing, y - ascent]

Its width is:

rbearing - lbearing

Its height is:

ascent + descent

The origin for the next character is defined to be:

[x + width, y]

The lbearing member defines the extent of the left edge of the character ink
from the origin.
The rbearing member defines the extent of the right edge of the character ink
from the origin.
The ascent member defines the extent of the top edge of the character ink
from the origin.
The descent member defines the extent of the bottom edge of the character ink
from the origin.
The width member defines the logical width of the character.

Note that the baseline (the y position of the character origin)
is logically viewed as being the scanline just below nondescending characters.
When descent is zero,
only pixels with Y-coordinates less than y are drawn,
and the origin is logically viewed as being coincident with the left edge of
a nonkerned character.
When lbearing is zero,
no pixels with X-coordinate less than x are drawn.
Any of the
XCharStruct
metric members could be negative.
If the width is negative,
the next character will be placed to the left of the current origin.

The X protocol does not define the interpretation of the attributes member
in the
XCharStruct
structure.
A nonexistent character is represented with all members of its
XCharStruct
set to zero.

A font is not guaranteed to have any properties.
The interpretation of the property value (for example, long or unsigned long)
must be derived from a priori knowledge of the property.
A basic set of font properties is specified in the X Consortium standard
X Logical Font Description Conventions.

Loading and Freeing Fonts

Xlib provides functions that you can use to load fonts, get font information,
unload fonts, and free font information.
A few font functions use a
GContext
resource ID or a font ID interchangeably.

The
XLoadFont
function loads the specified font and returns its associated font ID.
If the font name is not in the Host Portable Character Encoding,
the result is implementation-dependent.
Use of uppercase or lowercase does not matter.
When the characters “?” and “*” are used in a font name, a
pattern match is performed and any matching font is used.
In the pattern,
the “?” character will match any single character,
and the “*” character will match any number of characters.
A structured format for font names is specified in the X Consortium standard
X Logical Font Description Conventions.
If
XLoadFont
was unsuccessful at loading the specified font,
a
BadName
error results.
Fonts are not associated with a particular screen
and can be stored as a component
of any GC.
When the font is no longer needed, call
XUnloadFont.

The
XQueryFont
function returns a pointer to the
XFontStruct
structure, which contains information associated with the font.
You can query a font or the font stored in a GC.
The font ID stored in the
XFontStruct
structure will be the
GContext
ID, and you need to be careful when using this ID in other functions
(see
XGContextFromGC).
If the font does not exist,
XQueryFont
returns NULL.
To free this data, use
XFreeFontInfo.

The
XLoadQueryFont
function provides the most common way for accessing a font.
XLoadQueryFont
both opens (loads) the specified font and returns a pointer to the
appropriate
XFontStruct
structure.
If the font name is not in the Host Portable Character Encoding,
the result is implementation-dependent.
If the font does not exist,
XLoadQueryFont
returns NULL.

The
XFreeFont
function deletes the association between the font resource ID and the specified
font and frees the
XFontStruct
structure.
The font itself will be freed when no other resource references it.
The data and the font should not be referenced again.

Given the atom for that property,
the
XGetFontProperty
function returns the value of the specified font property.
XGetFontProperty
also returns
False
if the property was not defined or
True
if it was defined.
A set of predefined atoms exists for font properties,
which can be found in
<X11/Xatom.h>.
This set contains the standard properties associated with
a font.
Although it is not guaranteed,
it is likely that the predefined font properties will be present.

The
XUnloadFont
function deletes the association between the font resource ID and the specified font.
The font itself will be freed when no other resource references it.
The font should not be referenced again.

Specifies the null-terminated pattern string that can contain wildcard
characters.

maxnames

Specifies the maximum number of names to be returned.

actual_count_return

Returns the actual number of font names.

The
XListFonts
function returns an array of available font names
(as controlled by the font search path; see
XSetFontPath)
that match the string you passed to the pattern argument.
The pattern string can contain any characters,
but each asterisk (*) is a wildcard for any number of characters,
and each question mark (?) is a wildcard for a single character.
If the pattern string is not in the Host Portable Character Encoding,
the result is implementation-dependent.
Use of uppercase or lowercase does not matter.
Each returned string is null-terminated.
If the data returned by the server is in the Latin Portable Character Encoding,
then the returned strings are in the Host Portable Character Encoding.
Otherwise, the result is implementation-dependent.
If there are no matching font names,
XListFonts
returns NULL.
The client should call
XFreeFontNames
when finished with the result to free the memory.

Specifies the null-terminated pattern string that can contain wildcard
characters.

maxnames

Specifies the maximum number of names to be returned.

count_return

Returns the actual number of matched font names.

info_return

Returns the font information.

The
XListFontsWithInfo
function returns a list of font names that match the specified pattern and their
associated font information.
The list of names is limited to size specified by maxnames.
The information returned for each font is identical to what
XLoadQueryFont
would return except that the per-character metrics are not returned.
The pattern string can contain any characters,
but each asterisk (*) is a wildcard for any number of characters,
and each question mark (?) is a wildcard for a single character.
If the pattern string is not in the Host Portable Character Encoding,
the result is implementation-dependent.
Use of uppercase or lowercase does not matter.
Each returned string is null-terminated.
If the data returned by the server is in the Latin Portable Character Encoding,
then the returned strings are in the Host Portable Character Encoding.
Otherwise, the result is implementation-dependent.
If there are no matching font names,
XListFontsWithInfo
returns NULL.

To free only the allocated name array,
the client should call
XFreeFontNames.
To free both the name array and the font information array
or to free just the font information array,
the client should call
XFreeFontInfo.

The
XFreeFontInfo
function frees a font structure or an array of font structures
and optionally an array of font names.
If NULL is passed for names, no font names are freed.
If a font structure for an open font (returned by
XLoadQueryFont)
is passed, the structure is freed,
but the font is not closed; use
XUnloadFont
to close the font.

Computing Character String Sizes

Xlib provides functions that you can use to compute the width,
the logical extents,
and the server information about 8-bit and 2-byte text strings.
The width is computed by adding the character widths of all the characters.
It does not matter if the font is an 8-bit or 2-byte font.
These functions return the sum of the character metrics in pixels.

The ascent member is set to the maximum of the ascent metrics of all
characters in the string.
The descent member is set to the maximum of the descent metrics.
The width member is set to the sum of the character-width metrics of all
characters in the string.
For each character in the string,
let W be the sum of the character-width metrics of all characters preceding
it in the string.
Let L be the left-side-bearing metric of the character plus W.
Let R be the right-side-bearing metric of the character plus W.
The lbearing member is set to the minimum L of all characters in the string.
The rbearing member is set to the maximum R.

For fonts defined with linear indexing rather than 2-byte matrix indexing,
each
XChar2b
structure is interpreted as a 16-bit number with byte1 as the
most significant byte.
If the font has no defined default character,
undefined characters in the string are taken to have all zero metrics.

Querying Character String Sizes

To query the server for the bounding box of an 8-bit character string in a
given font, use
XQueryTextExtents.

Specifies either the font ID or the
GContext
ID that contains the font.

string

Specifies the character string.

nchars

Specifies the number of characters in the character string.

direction_return

Returns the value of the direction hint
(FontLeftToRight
or
FontRightToLeft).

font_ascent_return

Returns the font ascent.

font_descent_return

Returns the font descent.

overall_return

Returns the overall size in the specified
XCharStruct
structure.

The
XQueryTextExtents
and
XQueryTextExtents16
functions return the bounding box of the specified 8-bit and 16-bit
character string in the specified font or the font contained in the
specified GC.
These functions query the X server and, therefore, suffer the round-trip
overhead that is avoided by
XTextExtents
and
XTextExtents16.
Both functions return a
XCharStruct
structure, whose members are set to the values as follows.

The ascent member is set to the maximum of the ascent metrics
of all characters in the string.
The descent member is set to the maximum of the descent metrics.
The width member is set to the sum of the character-width metrics
of all characters in the string.
For each character in the string,
let W be the sum of the character-width metrics of all characters preceding
it in the string.
Let L be the left-side-bearing metric of the character plus W.
Let R be the right-side-bearing metric of the character plus W.
The lbearing member is set to the minimum L of all characters in the string.
The rbearing member is set to the maximum R.

For fonts defined with linear indexing rather than 2-byte matrix indexing,
each
XChar2b
structure is interpreted as a 16-bit number with byte1 as the
most significant byte.
If the font has no defined default character,
undefined characters in the string are taken to have all zero metrics.

Characters with all zero metrics are ignored.
If the font has no defined default_char,
the undefined characters in the string are also ignored.

If the font member is not
None,
the font is changed before printing and also is stored in the GC.
If an error was generated during text drawing,
the previous items may have been drawn.
The baseline of the characters are drawn starting at the x and y
coordinates that you pass in the text drawing functions.

For example, consider the background rectangle drawn by
XDrawImageString.
If you want the upper-left corner of the background rectangle
to be at pixel coordinate (x,y), pass the (x,y + ascent)
as the baseline origin coordinates to the text functions.
The ascent is the font ascent, as given in the
XFontStruct
structure.
If you want the lower-left corner of the background rectangle
to be at pixel coordinate (x,y), pass the (x,y - descent + 1)
as the baseline origin coordinates to the text functions.
The descent is the font descent, as given in the
XFontStruct
structure.

The
XDrawText16
function is similar to
XDrawText
except that it uses 2-byte or 16-bit characters.
Both functions allow complex spacing and font shifts between counted strings.

Each text item is processed in turn.
A font member other than
None
in an item causes the font to be stored in the GC
and used for subsequent text.
A text element delta specifies an additional change
in the position along the x axis before the string is drawn.
The delta is always added to the character origin
and is not dependent on any characteristics of the font.
Each character image, as defined by the font in the GC, is treated as an
additional mask for a fill operation on the drawable.
The drawable is modified only where the font character has a bit set to 1.
If a text item generates a
BadFont
error, the previous text items may have been drawn.

For fonts defined with linear indexing rather than 2-byte matrix indexing,
each
XChar2b
structure is interpreted as a 16-bit number with byte1 as the
most significant byte.

Both functions use these GC components:
function, plane-mask, fill-style, font, subwindow-mode,
clip-x-origin, clip-y-origin, and clip-mask.
They also use these GC mode-dependent components:
foreground, background, tile, stipple, tile-stipple-x-origin,
and tile-stipple-y-origin.

Each character image, as defined by the font in the GC, is treated as an
additional mask for a fill operation on the drawable.
The drawable is modified only where the font character has a bit set to 1.
For fonts defined with 2-byte matrix indexing
and used with
XDrawString16,
each byte is used as a byte2 with a byte1 of zero.

Both functions use these GC components:
function, plane-mask, fill-style, font, subwindow-mode, clip-x-origin,
clip-y-origin, and clip-mask.
They also use these GC mode-dependent components:
foreground, background, tile, stipple, tile-stipple-x-origin,
and tile-stipple-y-origin.

Drawing Image Text Characters

Some applications, in particular terminal emulators, need to
print image text in which both the foreground and background bits of
each character are painted.
This prevents annoying flicker on many displays.

The
XDrawImageString16
function is similar to
XDrawImageString
except that it uses 2-byte or 16-bit characters.
Both functions also use both the foreground and background pixels
of the GC in the destination.

The effect is first to fill a
destination rectangle with the background pixel defined in the GC and then
to paint the text with the foreground pixel.
The upper-left corner of the filled rectangle is at:

[x, y - font-ascent]

The width is:

overall-width

The height is:

font-ascent + font-descent

The overall-width, font-ascent, and font-descent
are as would be returned by
XQueryTextExtents
using gc and string.
The function and fill-style defined in the GC are ignored for these functions.
The effective function is
GXcopy,
and the effective fill-style is
FillSolid.

For fonts defined with 2-byte matrix indexing
and used with
XDrawImageString,
each byte is used as a byte2 with a byte1 of zero.

Transferring Images between Client and Server

Xlib provides functions that you can use to transfer images between a client
and the server.
Because the server may require diverse data formats,
Xlib provides an image object that fully describes the data in memory
and that provides for basic operations on that data.
You should reference the data
through the image object rather than referencing the data directly.
However, some implementations of the Xlib library may efficiently deal with
frequently used data formats by replacing
functions in the procedure vector with special case functions.
Supported operations include destroying the image, getting a pixel,
storing a pixel, extracting a subimage of an image, and adding a constant
to an image (see section 16.8).

All the image manipulation functions discussed in this section make use of
the
XImage
structure,
which describes an image as it exists in the client's memory.

To initialize the image manipulation routines of an image structure, use
XInitImage.

Status XInitImage(XImage *image);

ximage

Specifies the image.

The
XInitImage
function initializes the internal image manipulation routines of an
image structure, based on the values of the various structure members.
All fields other than the manipulation routines must already be initialized.
If the bytes_per_line member is zero,
XInitImage
will assume the image data is contiguous in memory and set the
bytes_per_line member to an appropriate value based on the other
members; otherwise, the value of bytes_per_line is not changed.
All of the manipulation routines are initialized to functions
that other Xlib image manipulation functions need to operate on the
type of image specified by the rest of the structure.

This function must be called for any image constructed by the client
before passing it to any other Xlib function.
Image structures created or returned by Xlib do not need to be
initialized in this fashion.

This function returns a nonzero status if initialization of the
structure is successful. It returns zero if it detected some error
or inconsistency in the structure, in which case the image is not changed.

To combine an image with a rectangle of a drawable on the display,
use
XPutImage.

Specifies the offset in X from the left edge of the image defined
by the
XImage
structure.

src_y

Specifies the offset in Y from the top edge of the image defined
by the
XImage
structure.
and are the coordinates of the subimage

dest_x

dest_y

Specify the x and y coordinates(Dx.

width

height

Specify the width and height(Wh.

The
XPutImage
function
combines an image with a rectangle of the specified drawable.
The section of the image defined by the src_x, src_y, width, and height
arguments is drawn on the specified part of the drawable.
If
XYBitmap
format is used, the depth of the image must be one,
or a
BadMatch
error results.
The foreground pixel in the GC defines the source for the one bits in the image,
and the background pixel defines the source for the zero bits.
For
XYPixmap
and
ZPixmap,
the depth of the image must match the depth of the drawable,
or a
BadMatch
error results.

If the characteristics of the image (for example, byte_order and bitmap_unit)
differ from what the server requires,
XPutImage
automatically makes the appropriate
conversions.

This function uses these GC components:
function, plane-mask, subwindow-mode, clip-x-origin, clip-y-origin,
and clip-mask.
It also uses these GC mode-dependent components:
foreground and background.

Specifies the drawable.
and define the upper-left corner of the rectangle

x

y

Specify the x and y coordinates(Xy.

width

height

Specify the width and height(Wh.

plane_mask

Specifies the plane mask.

format

Specifies the format for the image.
You can pass
XYPixmap
or
ZPixmap.

The
XGetImage
function returns a pointer to an
XImage
structure.
This structure provides you with the contents of the specified rectangle of
the drawable in the format you specify.
If the format argument is
XYPixmap,
the image contains only the bit planes you passed to the plane_mask argument.
If the plane_mask argument only requests a subset of the planes of the
display, the depth of the returned image will be the number of planes
requested.
If the format argument is
ZPixmap,
XGetImage
returns as zero the bits in all planes not
specified in the plane_mask argument.
The function performs no range checking on the values in plane_mask and ignores
extraneous bits.

XGetImage
returns the depth of the image to the depth member of the
XImage
structure.
The depth of the image is as specified when the drawable was created,
except when getting a subset of the planes in
XYPixmap
format, when the depth is given by the number of bits set to 1 in plane_mask.

If the drawable is a pixmap,
the given rectangle must be wholly contained within the pixmap,
or a
BadMatch
error results.
If the drawable is a window,
the window must be viewable,
and it must be the case that if there were no inferiors or overlapping windows,
the specified rectangle of the window would be fully visible on the screen
and wholly contained within the outside edges of the window,
or a
BadMatch
error results.
Note that the borders of the window can be included and read with
this request.
If the window has backing-store, the backing-store contents are
returned for regions of the window that are obscured by noninferior
windows.
If the window does not have backing-store,
the returned contents of such obscured regions are undefined.
The returned contents of visible regions of inferiors
of a different depth than the specified window's depth are also undefined.
The pointer cursor image is not included in the returned contents.
If a problem occurs,
XGetImage
returns NULL.

Specifies the drawable.
and define the upper-left corner of the rectangle

x

y

Specify the x and y coordinates(Xy.

width

height

Specify the width and height(Wh.

plane_mask

Specifies the plane mask.

format

Specifies the format for the image.
You can pass
XYPixmap
or
ZPixmap.

dest_image

Specifies the destination image.
specify its upper-left corner, and determine where the subimage \
is placed in the destination image

dest_x

dest_y

Specify the x and y coordinates(Dx.

The
XGetSubImage
function updates dest_image with the specified subimage in the same manner as
XGetImage.
If the format argument is
XYPixmap,
the image contains only the bit planes you passed to the plane_mask argument.
If the format argument is
ZPixmap,
XGetSubImage
returns as zero the bits in all planes not
specified in the plane_mask argument.
The function performs no range checking on the values in plane_mask and ignores
extraneous bits.
As a convenience,
XGetSubImage
returns a pointer to the same
XImage
structure specified by dest_image.

The depth of the destination
XImage
structure must be the same as that of the drawable.
If the specified subimage does not fit at the specified location
on the destination image, the right and bottom edges are clipped.
If the drawable is a pixmap,
the given rectangle must be wholly contained within the pixmap,
or a
BadMatch
error results.
If the drawable is a window,
the window must be viewable,
and it must be the case that if there were no inferiors or overlapping windows,
the specified rectangle of the window would be fully visible on the screen
and wholly contained within the outside edges of the window,
or a
BadMatch
error results.
If the window has backing-store,
then the backing-store contents are returned for regions of the window
that are obscured by noninferior windows.
If the window does not have backing-store,
the returned contents of such obscured regions are undefined.
The returned contents of visible regions of inferiors
of a different depth than the specified window's depth are also undefined.
If a problem occurs,
XGetSubImage
returns NULL.

Although it is difficult to categorize functions as exclusively for an application,
a window manager, or a session manager, the functions in this chapter are most
often used by window managers and session managers. It is not expected that
these functions will be used by most application programs. Xlib provides
management functions to:

Change the parent of a window

Control the lifetime of a window

Manage installed colormaps

Set and retrieve the font search path

Grab the server

Kill a client

Control the screen saver

Control host access

Changing the Parent of a Window

To change a window's parent to another window on the same screen, use
XReparentWindow.
There is no way to move a window between screens.

XReparentWindow(Display *display, Window w, Window parent, intx, y);

display

Specifies the connection to the X server.

w

Specifies the window.

parent

Specifies the parent window.

x

y

Specify the x and y coordinates(Xy.

If the specified window is mapped,
XReparentWindow
automatically performs an
UnmapWindow
request on it, removes it from its current position in the hierarchy,
and inserts it as the child of the specified parent.
The window is placed in the stacking order on top with respect to
sibling windows.

After reparenting the specified window,
XReparentWindow
causes the X server to generate a
ReparentNotify
event.
The override_redirect member returned in this event is
set to the window's corresponding attribute.
Window manager clients usually should ignore this window if this member
is set to
True.
Finally, if the specified window was originally mapped,
the X server automatically performs a
MapWindow
request on it.

The X server performs normal exposure processing on formerly obscured
windows.
The X server might not generate
Expose
events for regions from the initial
UnmapWindow
request that are immediately obscured by the final
MapWindow
request.
A
BadMatch
error results if:

The new parent window is not on the same screen as
the old parent window.

The new parent window is the specified window or an inferior of the
specified window.

The new parent is
InputOnly,
and the window is not.

The specified window has a
ParentRelative
background, and the new parent window is not the same depth as the
specified window.

Controlling the Lifetime of a Window

The save-set of a client is a list of other clients' windows that,
if they are inferiors of one of the client's windows at connection close,
should not be destroyed and should be remapped if they are unmapped.
For further information about close-connection processing,
see section 2.6.
To allow an application's window to survive when a window manager that
has reparented a window fails,
Xlib provides the save-set functions that you can
use to control the longevity of subwindows
that are normally destroyed when the parent is destroyed.
For example, a window manager that wants to add decoration
to a window by adding a frame might reparent an application's
window.
When the frame is destroyed,
the application's window should not be destroyed
but be returned to its previous place in the window hierarchy.

The X server automatically removes windows from the save-set
when they are destroyed.

To add or remove a window from the client's save-set, use
XChangeSaveSet.

XChangeSaveSet(Display *display, Window w, int change_mode);

display

Specifies the connection to the X server.

w

Specifies the window (Wi.

change_mode

Specifies the mode.
You can pass
SetModeInsert
or
SetModeDelete.

Depending on the specified mode,
XChangeSaveSet
either inserts or deletes the specified window from the client's save-set.
The specified window must have been created by some other client,
or a
BadMatch
error results.

Managing Installed Colormaps

The X server maintains a list of installed colormaps.
Windows using these colormaps are guaranteed to display with
correct colors; windows using other colormaps may or may not display
with correct colors.
Xlib provides functions that you can use to install a colormap,
uninstall a colormap, and obtain a list of installed colormaps.

At any time,
there is a subset of the installed maps that is viewed as an ordered list
and is called the required list.
The length of the required list is at most M,
where M is the minimum number of installed colormaps specified for the screen
in the connection setup.
The required list is maintained as follows.
When a colormap is specified to
XInstallColormap,
it is added to the head of the list;
the list is truncated at the tail, if necessary, to keep its length to
at most M.
When a colormap is specified to
XUninstallColormap
and it is in the required list,
it is removed from the list.
A colormap is not added to the required list when it is implicitly installed
by the X server,
and the X server cannot implicitly uninstall a colormap that is in the
required list.

If the specified colormap is not already an installed colormap,
the X server generates a
ColormapNotify
event on each window that has that colormap.
In addition, for every other colormap that is installed as
a result of a call to
XInstallColormap,
the X server generates a
ColormapNotify
event on each window that has that colormap.

The
XUninstallColormap
function removes the specified colormap from the required
list for its screen.
As a result,
the specified colormap might be uninstalled,
and the X server might implicitly install or uninstall additional colormaps.
Which colormaps get installed or uninstalled is server dependent
except that the required list must remain installed.

If the specified colormap becomes uninstalled,
the X server generates a
ColormapNotify
event on each window that has that colormap.
In addition, for every other colormap that is installed or uninstalled as a
result of a call to
XUninstallColormap,
the X server generates a
ColormapNotify
event on each window that has that colormap.

The
XListInstalledColormaps
function returns a list of the currently installed colormaps for the screen
of the specified window.
The order of the colormaps in the list is not significant
and is no explicit indication of the required list.
When the allocated list is no longer needed,
free it by using
.

Specifies the directory path used to look for a font.
Setting the path to the empty list restores the default path defined
for the X server.

ndirs

Specifies the number of directories in the path.

The
XSetFontPath
function defines the directory search path for font lookup.
There is only one search path per X server, not one per client.
The encoding and interpretation of the strings are implementation-dependent,
but typically they specify directories or font servers to be searched
in the order listed.
An X server is permitted to cache font information internally;
for example, it might cache an entire font from a file and not
check on subsequent opens of that font to see if the underlying
font file has changed.
However,
when the font path is changed,
the X server is guaranteed to flush all cached information about fonts
for which there currently are no explicit resource IDs allocated.
The meaning of an error from this request is implementation-dependent.

The
XGetFontPath
function allocates and returns an array of strings containing the search path.
The contents of these strings are implementation-dependent
and are not intended to be interpreted by client applications.
When it is no longer needed,
the data in the font path should be freed by using
XFreeFontPath.

Grabbing the Server

Xlib provides functions that you can use to grab and ungrab the server.
These functions can be used to control processing of output on other
connections by the window system server.
While the server is grabbed,
no processing of requests or close downs on any other connection will occur.
A client closing its connection automatically ungrabs the server.
Although grabbing the server is highly discouraged, it is sometimes necessary.

The
XGrabServer
function disables processing of requests and close downs on all other
connections than the one this request arrived on.
You should not grab the X server any more than is absolutely necessary.

The
XUngrabServer
function restarts processing of requests and close downs on other connections.
You should avoid grabbing the X server as much as possible.

Killing Clients

Xlib provides a function to cause the connection to
a client to be closed and its resources to be destroyed.
To destroy a client, use
XKillClient.

XKillClient(Display *display, XID resource);

display

Specifies the connection to the X server.

resource

Specifies any resource associated with the client that you want to destroy or
AllTemporary.

The
XKillClient
function
forces a close down of the client
that created the resource
if a valid resource is specified.
If the client has already terminated in
either
RetainPermanent
or
RetainTemporary
mode, all of the client's
resources are destroyed.
If
AllTemporary
is specified, the resources of all clients that have terminated in
RetainTemporary
are destroyed (see section 2.5).
This permits implementation of window manager facilities that aid debugging.
A client can set its close-down mode to
RetainTemporary.
If the client then crashes,
its windows would not be destroyed.
The programmer can then inspect the application's window tree
and use the window manager to destroy the zombie windows.

Specifies how to enable screen blanking.
You can pass
DontPreferBlanking,
PreferBlanking,
or
DefaultBlanking.

allow_exposures

Specifies the screen save control values.
You can pass
DontAllowExposures,
AllowExposures,
or
DefaultExposures.

Timeout and interval are specified in seconds.
A timeout of 0 disables the screen saver
(but an activated screen saver is not deactivated),
and a timeout of −1 restores the default.
Other negative values generate a
BadValue
error.
If the timeout value is nonzero,
XSetScreenSaver
enables the screen saver.
An interval of 0 disables the random-pattern motion.
If no input from devices (keyboard, mouse, and so on) is generated
for the specified number of timeout seconds once the screen saver is enabled,
the screen saver is activated.

For each screen,
if blanking is preferred and the hardware supports video blanking,
the screen simply goes blank.
Otherwise, if either exposures are allowed or the screen can be regenerated
without sending
Expose
events to clients,
the screen is tiled with the root window background tile randomly
re-origined each interval seconds.
Otherwise, the screens' state do not change,
and the screen saver is not activated.
The screen saver is deactivated,
and all screen states are restored at the next
keyboard or pointer input or at the next call to
XForceScreenSaver
with mode
ScreenSaverReset.

If the server-dependent screen saver method supports periodic change,
the interval argument serves as a hint about how long the change period
should be, and zero hints that no periodic change should be made.
Examples of ways to change the screen include scrambling the colormap
periodically, moving an icon image around the screen periodically, or tiling
the screen with the root window background tile, randomly re-origined
periodically.

Specifies the mode that is to be applied.
You can pass
ScreenSaverActive
or
ScreenSaverReset.

If the specified mode is
ScreenSaverActive
and the screen saver currently is deactivated,
XForceScreenSaver
activates the screen saver even if the screen saver had been disabled
with a timeout of zero.
If the specified mode is
ScreenSaverReset
and the screen saver currently is enabled,
XForceScreenSaver
deactivates the screen saver if it was activated,
and the activation timer is reset to its initial state
(as if device input had been received).

Returns the current screen blanking preference
(DontPreferBlanking,
PreferBlanking,
or
DefaultBlanking).

allow_exposures_return

Returns the current screen save control value
(DontAllowExposures,
AllowExposures,
or
DefaultExposures).

Controlling Host Access

This section discusses how to:

Add, get, or remove hosts from the access control list

Change, enable, or disable access

X does not provide any protection on a per-window basis.
If you find out the resource ID of a resource, you can manipulate it.
To provide some minimal level of protection, however,
connections are permitted only from machines you trust.
This is adequate on single-user workstations but obviously
breaks down on timesharing machines.
Although provisions exist in the X protocol for proper connection
authentication, the lack of a standard authentication server
leaves host-level access control as the only common mechanism.

The initial set of hosts allowed to open connections typically consists of:

The host the window system is running on.

On POSIX-conformant systems, each host listed in the
/etc/X?.hosts
file.
The ? indicates the number of the
display.
This file should consist of host names separated by newlines.
DECnet nodes must terminate in :: to distinguish them from Internet hosts.

If a host is not in the access control list when the access control
mechanism is enabled and if the host attempts to establish a connection,
the server refuses the connection.
To change the access list,
the client must reside on the same host as the server and/or must
have been granted permission in the initial authorization at connection
setup.

Servers also can implement other access control policies in addition to
or in place of this host access facility.
For further information about other access control implementations,
see X Window System Protocol.

Adding, Getting, or Removing Hosts

Xlib provides functions that you can use to add, get, or remove hosts
from the access control list.
All the host access control functions use the
XHostAddress
structure, which contains:

The family member specifies which protocol address family to use
(for example, TCP/IP or DECnet) and can be
FamilyInternet,
FamilyInternet6,
FamilyServerInterpreted,
FamilyDECnet,
or
FamilyChaos.
The length member specifies the length of the address in bytes.
The address member specifies a pointer to the address.

For TCP/IP, the address should be in network byte order.
For IP version 4 addresses, the family should be FamilyInternet
and the length should be 4 bytes. For IP version 6 addresses, the
family should be FamilyInternet6 and the length should be 16 bytes.

For the DECnet family,
the server performs no automatic swapping on the address bytes.
A Phase IV address is 2 bytes long.
The first byte contains the least significant 8 bits of the node number.
The second byte contains the most significant 2 bits of the
node number in the least significant 2 bits of the byte
and the area in the most significant 6 bits of the byte.

For the ServerInterpreted family, the length is ignored and the address
member is a pointer to a
XServerInterpretedAddress
structure, which contains:

The type and value members point to strings representing the type and value of
the server interpreted entry. These strings may not be NULL-terminated so care
should be used when accessing them. The typelength and valuelength members
specify the length in byte of the type and value strings.

The
XListHosts
function returns the current access control list as well as whether the use
of the list at connection setup was enabled or disabled.
XListHosts
allows a program to find out what machines can make connections.
It also returns a pointer to a list of host structures that
were allocated by the function.
When no longer needed,
this memory should be freed by calling
.

The
XRemoveHost
function removes the specified host from the access control list
for that display.
The server must be on the same host as the client process, or a
BadAccess
error results.
If you remove your machine from the access list,
you can no longer connect to that server,
and this operation cannot be reversed unless you reset the server.

The
XRemoveHosts
function removes each specified host from the access control list for that
display.
The X server must be on the same host as the client process, or a
BadAccess
error results.
If you remove your machine from the access list,
you can no longer connect to that server,
and this operation cannot be reversed unless you reset the server.

A client application communicates with the X server through the connection you establish with
the XOpenDisplay function. A client application sends requests to the X server over this
connection. These requests are made by the Xlib functions that are called in the client application.
Many Xlib functions cause the X server to generate events, and the user’s typing or moving the
pointer can generate events asynchronously. The X server returns events to the client on the same
connection.

Event Types

An event is data generated asynchronously by the X server as a result of some
device activity or as side effects of a request sent by an Xlib function.
Device-related events propagate from the source window to ancestor windows
until some client application has selected that event type
or until the event is explicitly discarded.
The X server generally sends an event to a client application
only if the client has specifically asked to be informed of that event type,
typically by setting the event-mask attribute of the window.
The mask can also be set when you create a window
or by changing the window's
event-mask.
You can also mask out events that would propagate to ancestor windows
by manipulating the
do-not-propagate mask of the window's attributes.
However,
MappingNotify
events are always sent to all clients.

An event type describes a specific event generated by the X server.
For each event type,
a corresponding constant name is defined in
<X11/X.h>,
which is used when referring to an event type.
The following table lists the event category
and its associated event type or types.
The processing associated with these events is discussed in section 10.5.

The type member is set to the event type constant name that uniquely identifies
it.
For example, when the X server reports a
GraphicsExpose
event to a client application, it sends an
XGraphicsExposeEvent
structure with the type member set to
GraphicsExpose.
The display member is set to a pointer to the display the event was read on.
The send_event member is set to
True
if the event came from a
SendEvent
protocol request.
The serial member is set from the serial number reported in the protocol
but expanded from the 16-bit least-significant bits to a full 32-bit value.
The window member is set to the window that is most useful to toolkit
dispatchers.

The X server can send events at any time in the input stream.
Xlib stores any events received while waiting for a reply in an event queue
for later use.
Xlib also provides functions that allow you to check events in the event queue
(see section 11.3).

In addition to the individual structures declared for each event type, the
XEvent
structure is a union of the individual structures declared for each event type.
Depending on the type,
you should access members of each event by using the
XEvent
union.

An
XEvent
structure's first entry always is the type member,
which is set to the event type.
The second member always is the serial number of the protocol request
that generated the event.
The third member always is send_event,
which is a
Bool
that indicates if the event was sent by a different client.
The fourth member always is a display,
which is the display that the event was read from.
Except for keymap events,
the fifth member always is a window,
which has been carefully selected to be useful to toolkit dispatchers.
To avoid breaking toolkits,
the order of these first five entries is not to change.
Most events also contain a time member,
which is the time at which an event occurred.
In addition, a pointer to the generic event must be cast before it
is used to access any other information in the structure.

Event Masks

Clients select event reporting of most events relative to a window.
To do this, pass an event mask to an Xlib event-handling
function that takes an event_mask argument.
The bits of the event mask are defined in
<X11/X.h>.
Each bit in the event mask maps to an event mask name,
which describes the event or events you want the X server to
return to a client application.

Unless the client has specifically asked for them,
most events are not reported to clients when they are generated.
Unless the client suppresses them by setting graphics-exposures in the GC to
False,
GraphicsExpose
and
NoExpose
are reported by default as a result of
XCopyPlane
and
XCopyArea.
SelectionClear,
SelectionRequest,
SelectionNotify,
or
ClientMessage
cannot be masked.
Selection-related events are only sent to clients cooperating
with selections
(see section 4.5).
When the keyboard or pointer mapping is changed,
MappingNotify
is always sent to clients.

The following table
lists the event mask constants you can pass to
the event_mask argument and
the circumstances in which you would want to specify the
event mask:

Event Mask

Circumstances

NoEventMask

No events wanted

KeyPressMask

Keyboard down events wanted

KeyReleaseMask

Keyboard up events wanted

ButtonPressMask

Pointer button down events wanted

ButtonReleaseMask

Pointer button up events wanted

EnterWindowMask

Pointer window entry events wanted

LeaveWindowMask

Pointer window leave events wanted

PointerMotionMask

Pointer motion events wanted

PointerMotionHintMask

Pointer motion hints wanted

Button1MotionMask

Pointer motion while button 1 down

Button2MotionMask

Pointer motion while button 2 down

Button3MotionMask

Pointer motion while button 3 down

Button4MotionMask

Pointer motion while button 4 down

Button5MotionMask

Pointer motion while button 5 down

ButtonMotionMask

Pointer motion while any button down

KeymapStateMask

Keyboard state wanted at window entry and focus in

ExposureMask

Any exposure wanted

VisibilityChangeMask

Any change in visibility wanted

StructureNotifyMask

Any change in window structure wanted

ResizeRedirectMask

Redirect resize of this window

SubstructureNotifyMask

Substructure notification wanted

SubstructureRedirectMask

Redirect structure requests on children

FocusChangeMask

Any change in input focus wanted

PropertyChangeMask

Any change in property wanted

ColormapChangeMask

Any change in colormap wanted

OwnerGrabButtonMask

Automatic grabs should activate with owner_events set to True

Event Processing Overview

The event reported to a client application during event processing
depends on which event masks you provide as the event-mask attribute
for a window.
For some event masks, there is a one-to-one correspondence between
the event mask constant and the event type constant.
For example, if you pass the event mask
ButtonPressMask,
the X server sends back only
ButtonPress
events.
Most events contain a time member,
which is the time at which an event occurred.

In other cases, one event mask constant can map to several event type constants.
For example, if you pass the event mask
SubstructureNotifyMask,
the X server can send back
CirculateNotify,
ConfigureNotify,
CreateNotify,
DestroyNotify,
GravityNotify,
MapNotify,
ReparentNotify,
or
UnmapNotify
events.

In another case,
two event masks can map to one event type.
For example,
if you pass either
PointerMotionMask
or
ButtonMotionMask,
the X server sends back
a
MotionNotify
event.

The following table
lists the event mask,
its associated event type or types,
and the structure name associated with the event type.
Some of these structures actually are typedefs to a generic structure
that is shared between two event types.
Note that N.A. appears in columns for which the information is not applicable.

Event Mask

Event Type

Structure

Generic Structure

ButtonMotionMask

Button1MotionMask

Button2MotionMask

Button3MotionMask

Button4MotionMask

Button5MotionMask

MotionNotify

XPointerMovedEvent

XMotionEvent

ButtonPressMask

ButtonPress

XButtonPressedEvent

XButtonEvent

ButtonReleaseMask

ButtonRelease

XButtonReleasedEvent

XButtonEvent

ColormapChangeMask

ColormapNotify

XColormapEvent

EnterWindowMask

EnterNotify

XEnterWindowEvent

XCrossingEvent

LeaveWindowMask

LeaveNotify

XLeaveWindowEvent

XCrossingEvent

ExposureMask

Expose

XExposeEvent

GCGraphicsExposures in GC

GraphicsExpose

XGraphicsExposeEvent

NoExpose

XNoExposeEvent

FocusChangeMask

FocusIn

XFocusInEvent

XFocusChangeEvent

FocusOut

XFocusOutEvent

XFocusChangeEvent

KeymapStateMask

KeymapNotify

XKeymapEvent

KeyPressMask

KeyPress

XKeyPressedEvent

XKeyEvent

KeyReleaseMask

KeyRelease

XKeyReleasedEvent

XKeyEvent

OwnerGrabButtonMask

N.A.

N.A.

PointerMotionMask

MotionNotify

XPointerMovedEvent

XMotionEvent

PointerMotionHintMask

N.A.

N.A.

PropertyChangeMask

PropertyNotify

XPropertyEvent

ResizeRedirectMask

ResizeRequest

XResizeRequestEvent

StructureNotifyMask

CirculateNotify

XCirculateEvent

ConfigureNotify

XConfigureEvent

DestroyNotify

XDestroyWindowEvent

GravityNotify

XGravityEvent

MapNotify

XMapEvent

ReparentNotify

XReparentEvent

UnmapNotify

XUnmapEvent

SubstructureNotifyMask

CirculateNotify

XCirculateEvent

ConfigureNotify

XConfigureEvent

CreateNotify

XCreateWindowEvent

DestroyNotify

XDestroyWindowEvent

GravityNotify

XGravityEvent

MapNotify

XMapEvent

ReparentNotify

XReparentEvent

UnmapNotify

XUnmapEvent

SubstructureRedirectMask

CirculateRequest

XCirculateRequestEvent

ConfigureRequest

XConfigureRequestEvent

MapRequest

XMapRequestEvent

N.A.

ClientMessage

XClientMessageEvent

N.A.

MappingNotify

XMappingEvent

N.A.

SelectionClear

XSelectionClearEvent

N.A.

SelectionNotify

XSelectionEvent

N.A.

SelectionRequest

XSelectionRequestEvent

VisibilityChangeMask

VisibilityNotify

XVisibilityEvent

The sections that follow describe the processing that occurs
when you select the different event masks.
The sections are organized according to these processing categories:

Keyboard and pointer events

Window crossing events

Input focus events

Keymap state notification events

Exposure events

Window state notification events

Structure control events

Colormap state notification events

Client communication events

Keyboard and Pointer Events

This section discusses:

Pointer button events

Keyboard and pointer events

Pointer Button Events

The following describes the event processing that occurs when a pointer button
press is processed with the pointer in some window w and
when no active pointer grab is in progress.

The X server searches the ancestors of w from the root down,
looking for a passive grab to activate.
If no matching passive grab on the button exists,
the X server automatically starts an active grab for the client receiving
the event and sets the last-pointer-grab time to the current server time.
The effect is essentially equivalent to an
XGrabButton
with these client passed arguments:

Argument

Value

w

The event window

event_mask

The client's selected pointer events on the event window

pointer_mode

GrabModeAsync

keyboard_mode

GrabModeAsync

owner_events

True,
if the client has selected
OwnerGrabButtonMask
on the event window,
otherwise
False

confine_to

None

cursor

None

The active grab is automatically terminated when
the logical state of the pointer has all buttons released.
Clients can modify the active grab by calling
XUngrabPointer
and
XChangeActivePointerGrab.

Keyboard and Pointer Events

This section discusses the processing that occurs for the
keyboard events
KeyPress
and
KeyRelease
and the pointer events
ButtonPress,
ButtonRelease,
and
MotionNotify.
For information about the keyboard event-handling utilities,
see chapter 11.

The X server reports
KeyPress
or
KeyRelease
events to clients wanting information about keys that logically change state.
Note that these events are generated for all keys,
even those mapped to modifier bits.
The X server reports
ButtonPress
or
ButtonRelease
events to clients wanting information about buttons that logically change state.

The X server reports
MotionNotify
events to clients wanting information about when the pointer logically moves.
The X server generates this event whenever the pointer is moved
and the pointer motion begins and ends in the window.
The granularity of
MotionNotify
events is not guaranteed,
but a client that selects this event type is guaranteed
to receive at least one event when the pointer moves and then rests.

The generation of the logical changes lags the physical changes
if device event processing is frozen.

To receive
KeyPress,
KeyRelease,
ButtonPress,
and
ButtonRelease
events, set
KeyPressMask,
KeyReleaseMask,
ButtonPressMask,
and
ButtonReleaseMask
bits in the event-mask attribute of the window.

To receive
MotionNotify
events, set one or more of the following event
masks bits in the event-mask attribute of the window.

Button1MotionMask - Button5MotionMask

The client application receives
MotionNotify
events only when one or more of the specified buttons is pressed.

ButtonMotionMask

The client application receives
MotionNotify
events only when at least one button is pressed.

PointerMotionMask

The client application receives
MotionNotify
events independent of the state of
the pointer buttons.

PointerMotionHintMask

If
PointerMotionHintMask
is selected in combination with one or more of the above masks,
the X server is free to send only one
MotionNotify
event (with the is_hint member of the
XPointerMovedEvent
structure set to
NotifyHint)
to the client for the event window,
until either the key or button state changes,
the pointer leaves the event window, or the client calls
XQueryPointer
or
.
The server still may send
MotionNotify
events without is_hint set to
NotifyHint.

The source of the event is the viewable window that the pointer is in.
The window used by the X server to report these events depends on
the window's position in the window hierarchy
and whether any intervening window prohibits the generation of these events.
Starting with the source window,
the X server searches up the window hierarchy until it locates the first
window specified by a client as having an interest in these events.
If one of the intervening windows has its do-not-propagate-mask
set to prohibit generation of the event type,
the events of those types will be suppressed.
Clients can modify the actual window used for reporting by performing
active grabs and, in the case of keyboard events, by using the focus window.

These structures have the following common members:
window, root, subwindow, time, x, y, x_root, y_root, state, and same_screen.
The window member is set to the window on which the
event was generated and is referred to as the event window.
As long as the conditions previously discussed are met,
this is the window used by the X server to report the event.
The root member is set to the source window's root window.
The x_root and y_root members are set to the pointer's coordinates
relative to the root window's origin at the time of the event.

The same_screen member is set to indicate whether the event
window is on the same screen
as the root window and can be either
True
or
False.
If
True,
the event and root windows are on the same screen.
If
False,
the event and root windows are not on the same screen.

If the source window is an inferior of the event window,
the subwindow member of the structure is set to the child of the event window
that is the source window or the child of the event window that is
an ancestor of the source window.
Otherwise, the X server sets the subwindow member to
None.
The time member is set to the time when the event was generated
and is expressed in milliseconds.

If the event window is on the same screen as the root window,
the x and y members
are set to the coordinates relative to the event window's origin.
Otherwise, these members are set to zero.

The state member is set to indicate the logical state of the pointer buttons
and modifier keys just prior to the event,
which is the bitwise inclusive OR of one or more of the
button or modifier key masks:
Button1Mask,
Button2Mask,
Button3Mask,
Button4Mask,
Button5Mask,
ShiftMask,
LockMask,
ControlMask,
Mod1Mask,
Mod2Mask,
Mod3Mask,
Mod4Mask,
and
Mod5Mask.

Each of these structures also has a member that indicates the detail.
For the
XKeyPressedEvent
and
XKeyReleasedEvent
structures, this member is called a keycode.
It is set to a number that represents a physical key on the keyboard.
The keycode is an arbitrary representation for any key on the keyboard
(see sections 12.7
and 16.1).

For the
XButtonPressedEvent
and
XButtonReleasedEvent
structures, this member is called button.
It represents the pointer button that changed state and can be the
Button1,
Button2,
Button3,
Button4,
or
Button5
value.
For the
XPointerMovedEvent
structure, this member is called is_hint.
It can be set to
NotifyNormal
or
NotifyHint.

Some of the symbols mentioned in this section have fixed values, as
follows:

Symbol

Value

Button1MotionMask

(1L<<8)

Button2MotionMask

(1L<<9)

Button3MotionMask

(1L<<10)

Button4MotionMask

(1L<<11)

Button5MotionMask

(1L<<12)

Button1Mask

(1<<8)

Button2Mask

(1<<9)

Button3Mask

(1<<10)

Button4Mask

(1<<11)

Button5Mask

(1<<12)

ShiftMask

(1<<0)

LockMask

(1<<1)

ControlMask

(1<<2)

Mod1Mask

(1<<3)

Mod2Mask

(1<<4)

Mod3Mask

(1<<5)

Mod4Mask

(1<<6)

Mod5Mask

(1<<7)

Button1

1

Button2

2

Button3

3

Button4

4

Button5

5

Window Entry/Exit Events

This section describes the processing that
occurs for the window crossing events
EnterNotify
and
LeaveNotify.
If a pointer motion or a window hierarchy change causes the
pointer to be in a different window than before, the X server reports
EnterNotify
or
LeaveNotify
events to clients who have selected for these events.
All
EnterNotify
and
LeaveNotify
events caused by a hierarchy change are
generated after any hierarchy event
(UnmapNotify,
MapNotify,
ConfigureNotify,
GravityNotify,
CirculateNotify)
caused by that change;
however, the X protocol does not constrain the ordering of
EnterNotify
and
LeaveNotify
events with respect to
FocusOut,
VisibilityNotify,
and
Expose
events.

This contrasts with
MotionNotify
events, which are also generated when the pointer moves
but only when the pointer motion begins and ends in a single window.
An
EnterNotify
or
LeaveNotify
event also can be generated when some client application calls
XGrabPointer
and
XUngrabPointer.

To receive
EnterNotify
or
LeaveNotify
events, set the
EnterWindowMask
or
LeaveWindowMask
bits of the event-mask attribute of the window.

The window member is set to the window on which the
EnterNotify
or
LeaveNotify
event was generated and is referred to as the event window.
This is the window used by the X server to report the event,
and is relative to the root
window on which the event occurred.
The root member is set to the root window of the screen
on which the event occurred.

For a
LeaveNotify
event,
if a child of the event window contains the initial position of the pointer,
the subwindow component is set to that child.
Otherwise, the X server sets the subwindow member to
None.
For an
EnterNotify
event, if a child of the event window contains the final pointer position,
the subwindow component is set to that child or
None.

The time member is set to the time when the event was generated
and is expressed in milliseconds.
The x and y members are set to the coordinates of the pointer position in
the event window.
This position is always the pointer's final position,
not its initial position.
If the event window is on the same
screen as the root window, x and y are the pointer coordinates
relative to the event window's origin.
Otherwise, x and y are set to zero.
The x_root and y_root members are set to the pointer's coordinates relative to the
root window's origin at the time of the event.

The same_screen member is set to indicate whether the event window is on the same screen
as the root window and can be either
True
or
False.
If
True,
the event and root windows are on the same screen.
If
False,
the event and root windows are not on the same screen.

The focus member is set to indicate whether the event window is the focus window or an
inferior of the focus window.
The X server can set this member to either
True
or
False.
If
True,
the event window is the focus window or an inferior of the focus window.
If
False,
the event window is not the focus window or an inferior of the focus window.

The state member is set to indicate the state of the pointer buttons and
modifier keys just prior to the
event.
The X server can set this member to the bitwise inclusive OR of one
or more of the button or modifier key masks:
Button1Mask,
Button2Mask,
Button3Mask,
Button4Mask,
Button5Mask,
ShiftMask,
LockMask,
ControlMask,
Mod1Mask,
Mod2Mask,
Mod3Mask,
Mod4Mask,
Mod5Mask.

The mode member is set to indicate whether the events are normal events,
pseudo-motion events
when a grab activates, or pseudo-motion events when a grab deactivates.
The X server can set this member to
NotifyNormal,
NotifyGrab,
or
NotifyUngrab.

The detail member is set to indicate the notify detail and can be
NotifyAncestor,
NotifyVirtual,
NotifyInferior,
NotifyNonlinear,
or
NotifyNonlinearVirtual.

Normal Entry/Exit Events

EnterNotify
and
LeaveNotify
events are generated when the pointer moves from
one window to another window.
Normal events are identified by
XEnterWindowEvent
or
XLeaveWindowEvent
structures whose mode member is set to
NotifyNormal.

When the pointer moves from window A to window B and A is an inferior of B,
the X server does the following:

It generates a
LeaveNotify
event on window A, with the detail member of the
XLeaveWindowEvent
structure set to
NotifyAncestor.

It generates a
LeaveNotify
event on each window between window A and window B, exclusive,
with the detail member of each
XLeaveWindowEvent
structure set to
NotifyVirtual.

It generates an
EnterNotify
event on window B, with the detail member of the
XEnterWindowEvent
structure set to
NotifyInferior.

When the pointer moves from window A to window B and B is an inferior of A,
the X server does the following:

It generates a
LeaveNotify
event on window A,
with the detail member of the
XLeaveWindowEvent
structure set to
NotifyInferior.

It generates an
EnterNotify
event on each window between window A and window B, exclusive, with the
detail member of each
XEnterWindowEvent
structure set to
NotifyVirtual.

It generates an
EnterNotify
event on window B, with the detail member of the
XEnterWindowEvent
structure set to
NotifyAncestor.

When the pointer moves from window A to window B
and window C is their least common ancestor,
the X server does the following:

It generates a
LeaveNotify
event on window A,
with the detail member of the
XLeaveWindowEvent
structure set to
NotifyNonlinear.

It generates a
LeaveNotify
event on each window between window A and window C, exclusive,
with the detail member of each
XLeaveWindowEvent
structure set to
NotifyNonlinearVirtual.

It generates an
EnterNotify
event on each window between window C and window B, exclusive,
with the detail member of each
XEnterWindowEvent
structure set to
NotifyNonlinearVirtual.

It generates an
EnterNotify
event on window B, with the detail member of the
XEnterWindowEvent
structure set to
NotifyNonlinear.

When the pointer moves from window A to window B on different screens,
the X server does the following:

It generates a
LeaveNotify
event on window A,
with the detail member of the
XLeaveWindowEvent
structure set to
NotifyNonlinear.

If window A is not a root window,
it generates a
LeaveNotify
event on each window above window A up to and including its root,
with the detail member of each
XLeaveWindowEvent
structure set to
NotifyNonlinearVirtual.

If window B is not a root window,
it generates an
EnterNotify
event on each window from window B's root down to but not including
window B, with the detail member of each
XEnterWindowEvent
structure set to
NotifyNonlinearVirtual.

It generates an
EnterNotify
event on window B, with the detail member of the
XEnterWindowEvent
structure set to
NotifyNonlinear.

Grab and Ungrab Entry/Exit Events

Pseudo-motion mode
EnterNotify
and
LeaveNotify
events are generated when a pointer grab activates or deactivates.
Events in which the pointer grab activates
are identified by
XEnterWindowEvent
or
XLeaveWindowEvent
structures whose mode member is set to
NotifyGrab.
Events in which the pointer grab deactivates
are identified by
XEnterWindowEvent
or
XLeaveWindowEvent
structures whose mode member is set to
NotifyUngrab
(see
XGrabPointer).

When a pointer grab activates after any initial warp into a confine_to
window and before generating any actual
ButtonPress
event that activates the grab,
G is the grab_window for the grab,
and P is the window the pointer is in,
the X server does the following:

It generates
EnterNotify
and
LeaveNotify
events (see section 10.6.1)
with the mode members of the
XEnterWindowEvent
and
XLeaveWindowEvent
structures set to
NotifyGrab.
These events are generated
as if the pointer were to suddenly warp from
its current position in P to some position in G.
However, the pointer does not warp, and the X server uses the pointer position
as both the initial and final positions for the events.

When a pointer grab deactivates after generating any actual
ButtonRelease
event that deactivates the grab,
G is the grab_window for the grab,
and P is the window the pointer is in,
the X server does the following:

It generates
EnterNotify
and
LeaveNotify
events (see section 10.6.1)
with the mode members of the
XEnterWindowEvent
and
XLeaveWindowEvent
structures set to
NotifyUngrab.
These events are generated as if the pointer were to suddenly warp from
some position in G to its current position in P.
However, the pointer does not warp, and the X server uses the
current pointer position as both the
initial and final positions for the events.

Input Focus Events

This section describes the processing that occurs for the input focus events
FocusIn
and
FocusOut.
The X server can report
FocusIn
or
FocusOut
events to clients wanting information about when the input focus changes.
The keyboard is always attached to some window
(typically, the root window or a top-level window),
which is called the focus window.
The focus window and the position of the pointer determine the window that
receives keyboard input.
Clients may need to know when the input focus changes
to control highlighting of areas on the screen.

To receive
FocusIn
or
FocusOut
events, set the
FocusChangeMask
bit in the event-mask attribute of the window.

The window member is set to the window on which the
FocusIn
or
FocusOut
event was generated.
This is the window used by the X server to report the event.
The mode member is set to indicate whether the focus events
are normal focus events,
focus events while grabbed,
focus events
when a grab activates, or focus events when a grab deactivates.
The X server can set the mode member to
NotifyNormal,
NotifyWhileGrabbed,
NotifyGrab,
or
NotifyUngrab.

All
FocusOut
events caused by a window unmap are generated after any
UnmapNotify
event; however, the X protocol does not constrain the ordering of
FocusOut
events with respect to
generated
EnterNotify,
LeaveNotify,
VisibilityNotify,
and
Expose
events.

Depending on the event mode,
the detail member is set to indicate the notify detail and can be
NotifyAncestor,
NotifyVirtual,
NotifyInferior,
NotifyNonlinear,
NotifyNonlinearVirtual,
NotifyPointer,
NotifyPointerRoot,
or
NotifyDetailNone.

Normal Focus Events and Focus Events While Grabbed

Normal focus events are identified by
XFocusInEvent
or
XFocusOutEvent
structures whose mode member is set to
NotifyNormal.
Focus events while grabbed are identified by
XFocusInEvent
or
XFocusOutEvent
structures whose mode member is set to
NotifyWhileGrabbed.
The X server processes normal focus and focus events while grabbed according to
the following:

When the focus moves from window A to window B, A is an inferior of B,
and the pointer is in window P,
the X server does the following:

It generates a
FocusOut
event on window A, with the detail member of the
XFocusOutEvent
structure set to
NotifyAncestor.

It generates a
FocusOut
event on each window between window A and window B, exclusive,
with the detail member of each
XFocusOutEvent
structure set to
NotifyVirtual.

It generates a
FocusIn
event on window B, with the detail member of the
XFocusOutEvent
structure set to
NotifyInferior.

If window P is an inferior of window B
but window P is not window A or an inferior or ancestor of window A,
it generates a
FocusIn
event on each window below window B, down to and including window P,
with the detail member of each
XFocusInEvent
structure set to
NotifyPointer.

When the focus moves from window A to window B, B is an inferior of A,
and the pointer is in window P,
the X server does the following:

If window P is an inferior of window A
but P is not an inferior of window B or an ancestor of B,
it generates a
FocusOut
event on each window from window P up to but not including window A,
with the detail member of each
XFocusOutEvent
structure set to
NotifyPointer.

It generates a
FocusOut
event on window A,
with the detail member of the
XFocusOutEvent
structure set to
NotifyInferior.

It generates a
FocusIn
event on each window between window A and window B, exclusive, with the
detail member of each
XFocusInEvent
structure set to
NotifyVirtual.

It generates a
FocusIn
event on window B, with the detail member of the
XFocusInEvent
structure set to
NotifyAncestor.

When the focus moves from window A to window B,
window C is their least common ancestor,
and the pointer is in window P,
the X server does the following:

If window P is an inferior of window A,
it generates a
FocusOut
event on each window from window P up to but not including window A,
with the detail member of the
XFocusOutEvent
structure set to
NotifyPointer.

It generates a
FocusOut
event on window A,
with the detail member of the
XFocusOutEvent
structure set to
NotifyNonlinear.

It generates a
FocusOut
event on each window between window A and window C, exclusive,
with the detail member of each
XFocusOutEvent
structure set to
NotifyNonlinearVirtual.

It generates a
FocusIn
event on each window between C and B, exclusive,
with the detail member of each
XFocusInEvent
structure set to
NotifyNonlinearVirtual.

It generates a
FocusIn
event on window B, with the detail member of the
XFocusInEvent
structure set to
NotifyNonlinear.

If window P is an inferior of window B, it generates a
FocusIn
event on each window below window B down to and including window P,
with the detail member of the
XFocusInEvent
structure set to
NotifyPointer.

When the focus moves from window A to window B on different screens
and the pointer is in window P,
the X server does the following:

If window P is an inferior of window A, it generates a
FocusOut
event on each window from window P up to but not including window A,
with the detail member of each
XFocusOutEvent
structure set to
NotifyPointer.

It generates a
FocusOut
event on window A,
with the detail member of the
XFocusOutEvent
structure set to
NotifyNonlinear.

If window A is not a root window,
it generates a
FocusOut
event on each window above window A up to and including its root,
with the detail member of each
XFocusOutEvent
structure set to
NotifyNonlinearVirtual.

If window B is not a root window,
it generates a
FocusIn
event on each window from window B's root down to but not including
window B, with the detail member of each
XFocusInEvent
structure set to
NotifyNonlinearVirtual.

It generates a
FocusIn
event on window B, with the detail member of each
XFocusInEvent
structure set to
NotifyNonlinear.

If window P is an inferior of window B, it generates a
FocusIn
event on each window below window B down to and including window P,
with the detail member of each
XFocusInEvent
structure set to
NotifyPointer.

When the focus moves from window A to
PointerRoot
(events sent to the window under the pointer)
or
None
(discard), and the pointer is in window P,
the X server does the following:

If window P is an inferior of window A, it generates a
FocusOut
event on each window from window P up to but not including window A,
with the detail member of each
XFocusOutEvent
structure set to
NotifyPointer.

It generates a
FocusOut
event on window A, with the detail member of the
XFocusOutEvent
structure set to
NotifyNonlinear.

If window A is not a root window,
it generates a
FocusOut
event on each window above window A up to and including its root,
with the detail member of each
XFocusOutEvent
structure set to
NotifyNonlinearVirtual.

It generates a
FocusIn
event on the root window of all screens, with the detail member of each
XFocusInEvent
structure set to
NotifyPointerRoot
(or
NotifyDetailNone).

If the new focus is
PointerRoot,
it generates a
FocusIn
event on each window from window P's root down to and including window P,
with the detail member of each
XFocusInEvent
structure set to
NotifyPointer.

When the focus moves from
PointerRoot
(events sent to the window under the pointer)
or
None
to window A, and the pointer is in window P,
the X server does the following:

If the old focus is
PointerRoot,
it generates a
FocusOut
event on each window from window P up to and including window P's root,
with the detail member of each
XFocusOutEvent
structure set to
NotifyPointer.

It generates a
FocusOut
event on all root windows,
with the detail member of each
XFocusOutEvent
structure set to
NotifyPointerRoot
(or
NotifyDetailNone).

If window A is not a root window,
it generates a
FocusIn
event on each window from window A's root down to but not including window A,
with the detail member of each
XFocusInEvent
structure set to
NotifyNonlinearVirtual.

It generates a
FocusIn
event on window A,
with the detail member of the
XFocusInEvent
structure set to
NotifyNonlinear.

If window P is an inferior of window A, it generates a
FocusIn
event on each window below window A down to and including window P,
with the detail member of each
XFocusInEvent
structure set to
NotifyPointer.

When the focus moves from
PointerRoot
(events sent to the window under the pointer)
to
None
(or vice versa), and the pointer is in window P,
the X server does the following:

If the old focus is
PointerRoot,
it generates a
FocusOut
event on each window from window P up to and including window P's root,
with the detail member of each
XFocusOutEvent
structure set to
NotifyPointer.

It generates a
FocusOut
event on all root windows,
with the detail member of each
XFocusOutEvent
structure set to either
NotifyPointerRoot
or
NotifyDetailNone.

It generates a
FocusIn
event on all root windows,
with the detail member of each
XFocusInEvent
structure set to
NotifyDetailNone
or
NotifyPointerRoot.

If the new focus is
PointerRoot,
it generates a
FocusIn
event on each window from window P's root down to and including window P,
with the detail member of each
XFocusInEvent
structure set to
NotifyPointer.

Focus Events Generated by Grabs

Focus events in which the keyboard grab activates
are identified by
XFocusInEvent
or
XFocusOutEvent
structures whose mode member is set to
NotifyGrab.
Focus events in which the keyboard grab deactivates
are identified by
XFocusInEvent
or
XFocusOutEvent
structures whose mode member is set to
NotifyUngrab
(see
XGrabKeyboard).

When a keyboard grab activates before generating any actual
KeyPress
event that activates the grab,
G is the grab_window, and F is the current focus,
the X server does the following:

It generates
FocusIn
and
FocusOut
events, with the mode members of the
XFocusInEvent
and
XFocusOutEvent
structures set to
NotifyGrab.
These events are generated
as if the focus were to change from
F to G.

When a keyboard grab deactivates after generating any actual
KeyRelease
event that deactivates the grab,
G is the grab_window, and F is the current focus,
the X server does the following:

It generates
FocusIn
and
FocusOut
events, with the mode members of the
XFocusInEvent
and
XFocusOutEvent
structures set to
NotifyUngrab.
These events are generated
as if the focus were to change from
G to F.

Key Map State Notification Events

The X server can report
KeymapNotify
events to clients that want information about changes in their keyboard state.

To receive
KeymapNotify
events, set the
KeymapStateMask
bit in the event-mask attribute of the window.
The X server generates this event immediately after every
EnterNotify
and
FocusIn
event.

The window member is not used but is present to aid some toolkits.
The key_vector member is set to the bit vector of the keyboard.
Each bit set to 1 indicates that the corresponding key
is currently pressed.
The vector is represented as 32 bytes.
Byte N (from 0) contains the bits for keys 8N to 8N + 7
with the least significant bit in the byte representing key 8N.

Exposure Events

The X protocol does not guarantee to preserve the contents of window
regions when
the windows are obscured or reconfigured.
Some implementations may preserve the contents of windows.
Other implementations are free to destroy the contents of windows
when exposed.
X expects client applications to assume the responsibility for
restoring the contents of an exposed window region.
(An exposed window region describes a formerly obscured window whose
region becomes visible.)
Therefore, the X server sends
Expose
events describing the window and the region of the window that has been exposed.
A naive client application usually redraws the entire window.
A more sophisticated client application redraws only the exposed region.

Expose Events

The X server can report
Expose
events to clients wanting information about when the contents of window regions
have been lost.
The circumstances in which the X server generates
Expose
events are not as definite as those for other events.
However, the X server never generates
Expose
events on windows whose class you specified as
InputOnly.
The X server can generate
Expose
events when no valid contents are available for regions of a window
and either the regions are visible,
the regions are viewable and the server is (perhaps newly) maintaining
backing store on the window,
or the window is not viewable but the server is (perhaps newly) honoring the
window's backing-store attribute of
Always
or
WhenMapped.
The regions decompose into an (arbitrary) set of rectangles,
and an
Expose
event is generated for each rectangle.
For any given window,
the X server guarantees to report contiguously
all of the regions exposed by some action that causes
Expose
events, such as raising a window.

To receive
Expose
events, set the
ExposureMask
bit in the event-mask attribute of the window.

The window member is set to the exposed (damaged) window.
The x and y members are set to the coordinates relative to the window's origin
and indicate the upper-left corner of the rectangle.
The width and height members are set to the size (extent) of the rectangle.
The count member is set to the number of
Expose
events that are to follow.
If count is zero, no more
Expose
events follow for this window.
However, if count is nonzero, at least that number of
Expose
events (and possibly more) follow for this window.
Simple applications that do not want to optimize redisplay by distinguishing
between subareas of its window can just ignore all
Expose
events with nonzero counts and perform full redisplays
on events with zero counts.

GraphicsExpose and NoExpose Events

The X server can report
GraphicsExpose
events to clients wanting information about when a destination region could not
be computed during certain graphics requests:
XCopyArea
or
XCopyPlane.
The X server generates this event whenever a destination region could not be
computed because of an obscured or out-of-bounds source region.
In addition, the X server guarantees to report contiguously all of the regions exposed by
some graphics request
(for example, copying an area of a drawable to a destination
drawable).

The X server generates a
NoExpose
event whenever a graphics request that might
produce a
GraphicsExpose
event does not produce any.
In other words, the client is really asking for a
GraphicsExpose
event but instead receives a
NoExpose
event.

To receive
GraphicsExpose
or
NoExpose
events, you must first set the graphics-exposure
attribute of the graphics context to
True.
You also can set the graphics-expose attribute when creating a graphics
context using
XCreateGC
or by calling
XSetGraphicsExposures.

Both structures have these common members: drawable, major_code, and minor_code.
The drawable member is set to the drawable of the destination region on
which the graphics request was to be performed.
The major_code member is set to the graphics request initiated by the client
and can be either
X_CopyArea
or
X_CopyPlane.
If it is
X_CopyArea,
a call to
XCopyArea
initiated the request.
If it is
X_CopyPlane,
a call to
XCopyPlane
initiated the request.
These constants are defined in
<X11/Xproto.h>.
The minor_code member,
like the major_code member,
indicates which graphics request was initiated by
the client.
However, the minor_code member is not defined by the core
X protocol and will be zero in these cases,
although it may be used by an extension.

The
XGraphicsExposeEvent
structure has these additional members: x, y, width, height, and count.
The x and y members are set to the coordinates relative to the drawable's origin
and indicate the upper-left corner of the rectangle.
The width and height members are set to the size (extent) of the rectangle.
The count member is set to the number of
GraphicsExpose
events to follow.
If count is zero, no more
GraphicsExpose
events follow for this window.
However, if count is nonzero, at least that number of
GraphicsExpose
events (and possibly more) are to follow for this window.

Window State Change Events

The following sections discuss:

CirculateNotify
events

ConfigureNotify
events

CreateNotify
events

DestroyNotify
events

GravityNotify
events

MapNotify
events

MappingNotify
events

ReparentNotify
events

UnmapNotify
events

VisibilityNotify
events

CirculateNotify Events

The X server can report
CirculateNotify
events to clients wanting information about when a window changes
its position in the stack.
The X server generates this event type whenever a window is actually restacked
as a result of a client application calling
XCirculateSubwindows,
XCirculateSubwindowsUp,
or
XCirculateSubwindowsDown.

To receive
CirculateNotify
events, set the
StructureNotifyMask
bit in the event-mask attribute of the window
or the
SubstructureNotifyMask
bit in the event-mask attribute of the parent window
(in which case, circulating any child generates an event).

The event member is set either to the restacked window or to its parent,
depending on whether
StructureNotify
or
SubstructureNotify
was selected.
The window member is set to the window that was restacked.
The place member is set to the window's position after the restack occurs and
is either
PlaceOnTop
or
PlaceOnBottom.
If it is
PlaceOnTop,
the window is now on top of all siblings.
If it is
PlaceOnBottom,
the window is now below all siblings.

ConfigureNotify Events

The X server can report
ConfigureNotify
events to clients wanting information about actual changes to a window's
state, such as size, position, border, and stacking order.
The X server generates this event type whenever one of the following configure
window requests made by a client application actually completes:

A window's size, position, border, and/or stacking order is reconfigured
by calling
XConfigureWindow.

To receive
ConfigureNotify
events, set the
StructureNotifyMask
bit in the event-mask attribute of the window or the
SubstructureNotifyMask
bit in the event-mask attribute of the parent window
(in which case, configuring any child generates an event).

The event member is set either to the reconfigured window or to its parent,
depending on whether
StructureNotify
or
SubstructureNotify
was selected.
The window member is set to the window whose size, position,
border, and/or stacking
order was changed.

The x and y members are set to the coordinates relative to the parent window's
origin and indicate the position of the upper-left outside corner of the window.
The width and height members are set to the inside size of the window,
not including
the border.
The border_width member is set to the width of the window's border, in pixels.

The above member is set to the sibling window and is used
for stacking operations.
If the X server sets this member to
None,
the window whose state was changed is on the bottom of the stack
with respect to sibling windows.
However, if this member is set to a sibling window,
the window whose state was changed is placed on top of this sibling window.

The override_redirect member is set to the override-redirect attribute of the
window.
Window manager clients normally should ignore this window if the
override_redirect member
is
True.

CreateNotify Events

The X server can report
CreateNotify
events to clients wanting information about creation of windows.
The X server generates this event whenever a client
application creates a window by calling
XCreateWindow
or
XCreateSimpleWindow.

To receive
CreateNotify
events, set the
SubstructureNotifyMask
bit in the event-mask attribute of the window.
Creating any children then generates an event.

The parent member is set to the created window's parent.
The window member specifies the created window.
The x and y members are set to the created window's coordinates relative
to the parent window's origin and indicate the position of the upper-left
outside corner of the created window.
The width and height members are set to the inside size of the created window
(not including the border) and are always nonzero.
The border_width member is set to the width of the created window's border, in pixels.
The override_redirect member is set to the override-redirect attribute of the
window.
Window manager clients normally should ignore this window
if the override_redirect member is
True.

DestroyNotify Events

The X server can report
DestroyNotify
events to clients wanting information about which windows are destroyed.
The X server generates this event whenever a client application destroys a
window by calling
XDestroyWindow
or
XDestroySubwindows.

The ordering of the
DestroyNotify
events is such that for any given window,
DestroyNotify
is generated on all inferiors of the window
before being generated on the window itself.
The X protocol does not constrain the ordering among
siblings and across subhierarchies.

To receive
DestroyNotify
events, set the
StructureNotifyMask
bit in the event-mask attribute of the window or the
SubstructureNotifyMask
bit in the event-mask attribute of the parent window
(in which case, destroying any child generates an event).

The event member is set either to the destroyed window or to its parent,
depending on whether
StructureNotify
or
SubstructureNotify
was selected.
The window member is set to the window that is destroyed.

GravityNotify Events

The X server can report
GravityNotify
events to clients wanting information about when a window is moved because of a
change in the size of its parent.
The X server generates this event whenever a client
application actually moves a child window as a result of resizing its parent by calling
XConfigureWindow,
XMoveResizeWindow,
or
XResizeWindow.

To receive
GravityNotify
events, set the
StructureNotifyMask
bit in the event-mask attribute of the window or the
SubstructureNotifyMask
bit in the event-mask attribute of the parent window
(in which case, any child that is moved because its parent has been resized
generates an event).

The event member is set either to the window that was moved or to its parent,
depending on whether
StructureNotify
or
SubstructureNotify
was selected.
The window member is set to the child window that was moved.
The x and y members are set to the coordinates relative to the
new parent window's origin
and indicate the position of the upper-left outside corner of the
window.

MapNotify Events

The X server can report
MapNotify
events to clients wanting information about which windows are mapped.
The X server generates this event type whenever a client application changes the
window's state from unmapped to mapped by calling
XMapWindow,
XMapRaised,
XMapSubwindows,
XReparentWindow,
or as a result of save-set processing.

To receive
MapNotify
events, set the
StructureNotifyMask
bit in the event-mask attribute of the window or the
SubstructureNotifyMask
bit in the event-mask attribute of the parent window
(in which case, mapping any child generates an event).

The event member is set either to the window that was mapped or to its parent,
depending on whether
StructureNotify
or
SubstructureNotify
was selected.
The window member is set to the window that was mapped.
The override_redirect member is set to the override-redirect attribute
of the window.
Window manager clients normally should ignore this window
if the override-redirect attribute is
True,
because these events usually are generated from pop-ups,
which override structure control.

MappingNotify Events

The X server reports
MappingNotify
events to all clients.
There is no mechanism to express disinterest in this event.
The X server generates this event type whenever a client application
successfully calls:

The request member is set to indicate the kind of mapping change that occurred
and can be
MappingModifier,
MappingKeyboard,
or
MappingPointer.
If it is
MappingModifier,
the modifier mapping was changed.
If it is
MappingKeyboard,
the keyboard mapping was changed.
If it is
MappingPointer,
the pointer button mapping was changed.
The first_keycode and count members are set only
if the request member was set to
MappingKeyboard.
The number in first_keycode represents the first number in the range
of the altered mapping,
and count represents the number of keycodes altered.

ReparentNotify Events

The X server can report
ReparentNotify
events to clients wanting information about changing a window's parent.
The X server generates this event whenever a client
application calls
XReparentWindow
and the window is actually reparented.

To receive
ReparentNotify
events, set the
StructureNotifyMask
bit in the event-mask attribute of the window or the
SubstructureNotifyMask
bit in the event-mask attribute of either the old or the new parent window
(in which case, reparenting any child generates an event).

The event member is set either to the reparented window
or to the old or the new parent, depending on whether
StructureNotify
or
SubstructureNotify
was selected.
The window member is set to the window that was reparented.
The parent member is set to the new parent window.
The x and y members are set to the reparented window's coordinates relative
to the new parent window's
origin and define the upper-left outer corner of the reparented window.
The override_redirect member is set to the override-redirect attribute of the
window specified by the window member.
Window manager clients normally should ignore this window
if the override_redirect member is
True.

UnmapNotify Events

The X server can report
UnmapNotify
events to clients wanting information about which windows are unmapped.
The X server generates this event type whenever a client application changes the
window's state from mapped to unmapped.

To receive
UnmapNotify
events, set the
StructureNotifyMask
bit in the event-mask attribute of the window or the
SubstructureNotifyMask
bit in the event-mask attribute of the parent window
(in which case, unmapping any child window generates an event).

The event member is set either to the unmapped window or to its parent,
depending on whether
StructureNotify
or
SubstructureNotify
was selected.
This is the window used by the X server to report the event.
The window member is set to the window that was unmapped.
The from_configure member is set to
True
if the event was generated as a result of a resizing of the window's parent when
the window itself had a win_gravity of
UnmapGravity.

VisibilityNotify Events

The X server can report
VisibilityNotify
events to clients wanting any change in the visibility of the specified window.
A region of a window is visible if someone looking at the screen can
actually see it.
The X server generates this event whenever the visibility changes state.
However, this event is never generated for windows whose class is
InputOnly.

All
VisibilityNotify
events caused by a hierarchy change are generated
after any hierarchy event
(UnmapNotify,
MapNotify,
ConfigureNotify,
GravityNotify,
CirculateNotify)
caused by that change. Any
VisibilityNotify
event on a given window is generated before any
Expose
events on that window, but it is not required that all
VisibilityNotify
events on all windows be generated before all
Expose
events on all windows.
The X protocol does not constrain the ordering of
VisibilityNotify
events with
respect to
FocusOut,
EnterNotify,
and
LeaveNotify
events.

To receive
VisibilityNotify
events, set the
VisibilityChangeMask
bit in the event-mask attribute of the window.

The window member is set to the window whose visibility state changes.
The state member is set to the state of the window's visibility and can be
VisibilityUnobscured,
VisibilityPartiallyObscured,
or
VisibilityFullyObscured.
The X server ignores all of a window's subwindows
when determining the visibility state of the window and processes
VisibilityNotify
events according to the following:

When the window changes state from partially obscured, fully obscured,
or not viewable to viewable and completely unobscured,
the X server generates the event with the state member of the
XVisibilityEvent
structure set to
VisibilityUnobscured.

When the window changes state from viewable and completely unobscured or
not viewable to viewable and partially obscured,
the X server generates the event with the state member of the
XVisibilityEvent
structure set to
VisibilityPartiallyObscured.

When the window changes state from viewable and completely unobscured,
viewable and partially obscured, or not viewable to viewable and
fully obscured,
the X server generates the event with the state member of the
XVisibilityEvent
structure set to
VisibilityFullyObscured.

Structure Control Events

This section discusses:

CirculateRequest
events

ConfigureRequest
events

MapRequest
events

ResizeRequest
events

CirculateRequest Events

The X server can report
CirculateRequest
events to clients wanting information about
when another client initiates a circulate window request
on a specified window.
The X server generates this event type whenever a client initiates a circulate
window request on a window and a subwindow actually needs to be restacked.
The client initiates a circulate window request on the window by calling
XCirculateSubwindows,
XCirculateSubwindowsUp,
or
XCirculateSubwindowsDown.

To receive
CirculateRequest
events, set the
SubstructureRedirectMask
in the event-mask attribute of the window.
Then, in the future,
the circulate window request for the specified window is not executed,
and thus, any subwindow's position in the stack is not changed.
For example, suppose a client application calls
XCirculateSubwindowsUp
to raise a subwindow to the top of the stack.
If you had selected
SubstructureRedirectMask
on the window, the X server reports to you a
CirculateRequest
event and does not raise the subwindow to the top of the stack.

The parent member is set to the parent window.
The window member is set to the subwindow to be restacked.
The place member is set to what the new position in the stacking order should be
and is either
PlaceOnTop
or
PlaceOnBottom.
If it is
PlaceOnTop,
the subwindow should be on top of all siblings.
If it is
PlaceOnBottom,
the subwindow should be below all siblings.

To receive
ConfigureRequest
events, set the
SubstructureRedirectMask
bit in the event-mask attribute of the window.
ConfigureRequest
events are generated when a
ConfigureWindow
protocol request is issued on a child window by another client.
For example, suppose a client application calls
XLowerWindow
to lower a window.
If you had selected
SubstructureRedirectMask
on the parent window and if the override-redirect attribute
of the window is set to
False,
the X server reports a
ConfigureRequest
event to you and does not lower the specified window.

The parent member is set to the parent window.
The window member is set to the window whose size, position, border width,
and/or stacking order is to be reconfigured.
The value_mask member indicates which components were specified in the
ConfigureWindow
protocol request.
The corresponding values are reported as given in the request.
The remaining values are filled in from the current geometry of the window,
except in the case of above (sibling) and detail (stack-mode),
which are reported as
None
and
Above,
respectively, if they are not given in the request.

MapRequest Events

The X server can report
MapRequest
events to clients wanting information about a different client's desire
to map windows.
A window is considered mapped when a map window request completes.
The X server generates this event whenever a different client initiates
a map window request on an unmapped window whose override_redirect member
is set to
False.
Clients initiate map window requests by calling
XMapWindow,
XMapRaised,
or
XMapSubwindows.

To receive
MapRequest
events, set the
SubstructureRedirectMask
bit in the event-mask attribute of the window.
This means another client's attempts to map a child window by calling one of
the map window request functions is intercepted, and you are sent a
MapRequest
instead.
For example, suppose a client application calls
XMapWindow
to map a window.
If you (usually a window manager) had selected
SubstructureRedirectMask
on the parent window and if the override-redirect attribute
of the window is set to
False,
the X server reports a
MapRequest
event to you
and does not map the specified window.
Thus, this event gives your window manager client the ability
to control the placement of subwindows.

The parent member is set to the parent window.
The window member is set to the window to be mapped.

ResizeRequest Events

The X server can report
ResizeRequest
events to clients wanting information about another client's attempts to change the
size of a window.
The X server generates this event whenever some other client attempts to change
the size of the specified window by calling
XConfigureWindow,
XResizeWindow,
or
XMoveResizeWindow.

To receive
ResizeRequest
events, set the
ResizeRedirect
bit in the event-mask attribute of the window.
Any attempts to change the size by other clients are then redirected.

The window member is set to the window whose size another
client attempted to change.
The width and height members are set to the inside size of the window,
excluding the border.

Colormap State Change Events

The X server can report
ColormapNotify
events to clients wanting information about when the colormap changes
and when a colormap is installed or uninstalled.
The X server generates this event type whenever a client application:

The window member is set to the window whose associated
colormap is changed, installed, or uninstalled.
For a colormap that is changed, installed, or uninstalled,
the colormap member is set to the colormap associated with the window.
For a colormap that is changed by a call to
XFreeColormap,
the colormap member is set to
None.
The new member is set to indicate whether the colormap
for the specified window was changed or installed or uninstalled
and can be
True
or
False.
If it is
True,
the colormap was changed.
If it is
False,
the colormap was installed or uninstalled.
The state member is always set to indicate whether the colormap is installed or
uninstalled and can be
ColormapInstalled
or
ColormapUninstalled.

Client Communication Events

This section discusses:

ClientMessage
events

PropertyNotify
events

SelectionClear
events

SelectionNotify
events

SelectionRequest
events

ClientMessage Events

The X server generates
ClientMessage
events only when a client calls the function
XSendEvent.

The message_type member is set to an atom that indicates how the data
should be interpreted by the receiving client.
The format member is set to 8, 16, or 32 and specifies whether the data
should be viewed as